Sefer Likutei Shoshanim gives a few reasons as to why the longer Bracha of Ahava Rabba is used instead. Among other reasons, he quotes the Rashbash as saying:

שהרי יש בה קבול מלכות שמים שהרי אומר ויחד לבבנו לאהבה את שמך, על כן לא תקנו לברך על שמע
The Mitzva of saying Shema includes other Mitzvos, such as accepting 'the yoke of Heaven'. Thus we use a broader, more encompassing Bracha.

He also quotes the Siach Hasadeh who writes that we don't make a bracha on saying the Shema, because it is inccluded already in the Birkas Hatorah that we should have already said.

Another answer he gives is that the very first Passuk - 'Shema Yisrael' is considered a Bracha!

Finally, he writes that according to the Shagas Aryeh, one doesn't make a Bracha on a Mitzva that is primarily a thought..

Sefer Likutei Shoshanim gives a few reasons as to why the longer Bracha of Ahava Rabba is used instead. Among other reasons, he quotes the Rashbash as saying:

The Mitzva of saying Shema includes other Mitzvos, such as accepting 'the yoke of Heaven'. Thus we use a broader, more encompassing Bracha. שהרי יש בה קבול מלכות שמים שהרי אומר ויחד לבבנו לאהבה את שמך, על כן לא תקנו לברך על שמע

He also quotes the Siach Hasadeh who writes that we don't make a bracha on saying the Shema, because it is inccluded already in the Birkas Hatorah that we should have already said. משום דסומכין על ברכת התורה כיון דבקריאת שמע תלמוד תורה נמי אית בה, ומקיים בזה ת״ת

Another answer he gives is that the very first Passuk - 'Shema Yisrael' is considered a Bracha! הואיל ונחשב כברכה ופסוק שמע ישראל יש בו הזכרת השם ונחשב כמלכות

Finally, he writes that according to the Shaagas Aryeh, one doesn't make a Bracha on a Mitzva that is primarily a thought.. הואיל ויוצאין בקריאת שמע בהרהור משום הכי לא תקנו ברכה שאין מברכים על מצוה שהיא בהרהור

Sefer Likutei Shoshanim gives a few reasons as to why the longer Bracha of Ahava Rabba is used instead. Among other reasons, he quotes the Rashbash as saying:
שהרי יש בה קבול מלכות שמים שהרי אומר ויחד לבבנו לאהבה את שמך, על כן לא תקנו לברך על שמע
The Mitzva of saying Shema includes other Mitzvos, such as accepting 'the yoke of Heaven'. Thus we use a broader, more encompassing Bracha.

He also quotes the Siach Hasadeh who writes that we don't make a bracha on saying the Shema, because it is inccluded already in the Birkas Hatorah that we should have already said.

Another answer he gives is that the very first Passuk - 'Shema Yisrael' is considered a Bracha!

Finally, he writes that according to the Shagas Aryeh, one doesn't make a Bracha on a Mitzva that is primarily a thought..

Sefer Likutei Shoshanim gives a few reasons as to why the longer Bracha of Ahava Rabba is used instead. Among other reasons, he quotes the Rashbash as saying:

שהרי יש בה קבול מלכות שמים שהרי אומר ויחד לבבנו לאהבה את שמך, על כן לא תקנו לברך על שמע
The Mitzva of saying Shema includes other Mitzvos, such as accepting 'the yoke of Heaven'. Thus we use a broader, more encompassing Bracha.

He also quotes the Siach Hasadeh who writes that we don't make a bracha on saying the Shema, because it is inccluded already in the Birkas Hatorah that we should have already said.

Another answer he gives is that the very first Passuk - 'Shema Yisrael' is considered a Bracha!

Finally, he writes that according to the Shagas Aryeh, one doesn't make a Bracha on a Mitzva that is primarily a thought..