3 better source suggested by DonielF
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Some congregations do sing on weekdays, particularly during p'sukei d'zimrah. But the melodies are more "basic" than those used on Shabbat. I once asked a rabbi about the musical differences (why not sing the nicer melodies every day?) and he said it's because we should elevate Shabbat. I can't cite a source for that (the rabbi I asked has moved away), but it's consistent with other things that we do to elevate Shabbat, like wearing our finest clothes and making more elaborate meals.

An additional, practical matter is that, as you said in the question, for weekday morning minyanim, at least some of the attendees have to get to work after. On Shabbat, on the other hand, where else do we have to be?

Note that when we add Hallel on a weekday (Rosh Chodesh, Chol HaMoed, Chanukah), many (most?) congregations do add singing there.

As for musical instruments, the Levites did play instruments during the temple service, and Arakhin 11a and Sukkah 50b recordsrecord a disagreement about whether the essence of music is the song (from the mouth) or the instruments, with the majority saying the latter. That is, instruments are secondary (and some say they were played by slaves, not Levites), while the song is essential. Since the destruction of the second temple, the rabbis forbade instrumental music in services, both as a sign of mourning for the temple and in response to Hellenistic influences.

Some congregations do sing on weekdays, particularly during p'sukei d'zimrah. But the melodies are more "basic" than those used on Shabbat. I once asked a rabbi about the musical differences (why not sing the nicer melodies every day?) and he said it's because we should elevate Shabbat. I can't cite a source for that (the rabbi I asked has moved away), but it's consistent with other things that we do to elevate Shabbat, like wearing our finest clothes and making more elaborate meals.

An additional, practical matter is that, as you said in the question, for weekday morning minyanim, at least some of the attendees have to get to work after. On Shabbat, on the other hand, where else do we have to be?

Note that when we add Hallel on a weekday (Rosh Chodesh, Chol HaMoed, Chanukah), many (most?) congregations do add singing there.

As for musical instruments, the Levites did play instruments during the temple service, and Sukkah 50b records a disagreement about whether the essence of music is the song (from the mouth) or the instruments, with the majority saying the latter. Since the destruction of the second temple, the rabbis forbade instrumental music in services, both as a sign of mourning for the temple and in response to Hellenistic influences.

Some congregations do sing on weekdays, particularly during p'sukei d'zimrah. But the melodies are more "basic" than those used on Shabbat. I once asked a rabbi about the musical differences (why not sing the nicer melodies every day?) and he said it's because we should elevate Shabbat. I can't cite a source for that (the rabbi I asked has moved away), but it's consistent with other things that we do to elevate Shabbat, like wearing our finest clothes and making more elaborate meals.

An additional, practical matter is that, as you said in the question, for weekday morning minyanim, at least some of the attendees have to get to work after. On Shabbat, on the other hand, where else do we have to be?

Note that when we add Hallel on a weekday (Rosh Chodesh, Chol HaMoed, Chanukah), many (most?) congregations do add singing there.

As for musical instruments, the Levites did play instruments during the temple service, and Arakhin 11a and Sukkah 50b record a disagreement about whether the essence of music is the song (from the mouth) or the instruments, with the majority saying the latter. That is, instruments are secondary (and some say they were played by slaves, not Levites), while the song is essential. Since the destruction of the second temple, the rabbis forbade instrumental music in services, both as a sign of mourning for the temple and in response to Hellenistic influences.

2 h/t Mordechai in comments
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Some congregations do sing on weekdays, particularly during p'sukei d'zimrah. But the melodies are more "basic" than those used on Shabbat. I once asked a rabbi about the musical differences (why not sing the nicer melodies every day?) and he said it's because we should elevate Shabbat. I can't cite a source for that (the rabbi I asked has moved away), but it's consistent with other things that we do to elevate Shabbat, like wearing our finest clothes and making more elaborate meals.

This is my own reasoning: for similar reasons we wouldn't want to use musical instruments on weekdays, because we can't use them on Shabbat and that would mean decreasing our celebration, which is even worse than keeping it the same every day.

An additional, practical matter is that, as you said in the question, for weekday morning minyanim, at least some of the attendees have to get to work after. On Shabbat, on the other hand, where else do we have to be?

Note that when we add Hallel on a weekday (Rosh Chodesh, Chol HaMoed, Chanukah), many (most?) congregations do add singing there.

As for musical instruments, the Levites did play instruments during the temple service, and Sukkah 50b records a disagreement about whether the essence of music is the song (from the mouth) or the instruments, with the majority saying the latter. Since the destruction of the second temple, the rabbis forbade instrumental music in services, both as a sign of mourning for the temple and in response to Hellenistic influences.

Some congregations do sing on weekdays, particularly during p'sukei d'zimrah. But the melodies are more "basic" than those used on Shabbat. I once asked a rabbi about the musical differences (why not sing the nicer melodies every day?) and he said it's because we should elevate Shabbat. I can't cite a source for that (the rabbi I asked has moved away), but it's consistent with other things that we do to elevate Shabbat, like wearing our finest clothes and making more elaborate meals.

This is my own reasoning: for similar reasons we wouldn't want to use musical instruments on weekdays, because we can't use them on Shabbat and that would mean decreasing our celebration, which is even worse than keeping it the same every day.

An additional, practical matter is that, as you said in the question, for weekday morning minyanim, at least some of the attendees have to get to work after. On Shabbat, on the other hand, where else do we have to be?

Note that when we add Hallel on a weekday (Rosh Chodesh, Chol HaMoed, Chanukah), many (most?) congregations do add singing there.

Some congregations do sing on weekdays, particularly during p'sukei d'zimrah. But the melodies are more "basic" than those used on Shabbat. I once asked a rabbi about the musical differences (why not sing the nicer melodies every day?) and he said it's because we should elevate Shabbat. I can't cite a source for that (the rabbi I asked has moved away), but it's consistent with other things that we do to elevate Shabbat, like wearing our finest clothes and making more elaborate meals.

An additional, practical matter is that, as you said in the question, for weekday morning minyanim, at least some of the attendees have to get to work after. On Shabbat, on the other hand, where else do we have to be?

Note that when we add Hallel on a weekday (Rosh Chodesh, Chol HaMoed, Chanukah), many (most?) congregations do add singing there.

As for musical instruments, the Levites did play instruments during the temple service, and Sukkah 50b records a disagreement about whether the essence of music is the song (from the mouth) or the instruments, with the majority saying the latter. Since the destruction of the second temple, the rabbis forbade instrumental music in services, both as a sign of mourning for the temple and in response to Hellenistic influences.

1
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Some congregations do sing on weekdays, particularly during p'sukei d'zimrah. But the melodies are more "basic" than those used on Shabbat. I once asked a rabbi about the musical differences (why not sing the nicer melodies every day?) and he said it's because we should elevate Shabbat. I can't cite a source for that (the rabbi I asked has moved away), but it's consistent with other things that we do to elevate Shabbat, like wearing our finest clothes and making more elaborate meals.

This is my own reasoning: for similar reasons we wouldn't want to use musical instruments on weekdays, because we can't use them on Shabbat and that would mean decreasing our celebration, which is even worse than keeping it the same every day.

An additional, practical matter is that, as you said in the question, for weekday morning minyanim, at least some of the attendees have to get to work after. On Shabbat, on the other hand, where else do we have to be?

Note that when we add Hallel on a weekday (Rosh Chodesh, Chol HaMoed, Chanukah), many (most?) congregations do add singing there.