Very little motivation for the typical munchkin pc, sure. But for a real, breathing character? Imagine a person with a greek identity, who had long suffered by being forced to use that barbaric foreign tongue, latin? I could imagine him being lauded by his Theban peers for restoring the "true place" of Greek in Hermetic language, even if it was no more powerful than Latin.
Language is an important aspect of culture. Look at how conquering nations have forced their languages on the conquered, and how re-assertion of nearly-dead languages has been a powerful cultural force in the modern world.
It does however divide the Theban tribunal from much of the rest of the Order. By relying on Ancient Greek they divide the Order. The motivation could be as you described above, or it could be considered entirely selfish, or perhaps snobbish. Language is indeed an important aspect of culture, by working Hermetic magic in another language they are establishing another subculture within the order.