I heard somewhere (I don't remember the details) that the Septuagint ceased to be read in the Jewish community. Why?
The specific type of Greek was not known to Jews anymore, and the text became corrupted. Originally, it was felt that the Koine translation of the Torah, and specifically only the Torah, was good enough. The Greek words had specific connotations and the translation was good enough for the majority of people to get all the different layers of understanding out of the text. Koine Greek eventually became unknown with the nuance required, the text became corrupted away from the original text of the 70 elders as the Greek text didn't get the same care as the Hebrew. So, Greek just degraded away to the point where it was ruled that it cannot be used anymore.
Tefillin and mezuzot may be written only in Assyrian script. Permission was granted to write Torah scrolls in Greek as well. That Greek language has, however, been forgotten from the world. It has been confused and has sunk into oblivion. Therefore, at present, all three sacred articles may be written using Assyrian script alone.
Rambam, Hilkhoth ST"M 1:19