According to what I gathered from the
archives, languages are, in fact, supposed to
evolve. And just like accents, this evolution would depend on location, leading to different variations of the same languages appearing. Over time, they would continue to drift apart from each other until speakers of different groups would not be able to understand each other.
The troubles this would bring are not, however, the reason why the gods are set against this. The
gods are obviously immortal. This means that, without intervention, language would keep changing around them, and they would have to constantly waste efforts to catch up to what's going on, otherwise they themselves would not be able to understand their own worshippers.
This is also why, if more mortals understood what's going on, most would agree with the gods' actions. Can you imagine not being able to pray directly to your gods, and share words of thanks or polite requests with them? Yes, scholars and priests would undoubtedly be able to speak the old tongue and communicate with the gods, but using them as intermediate would make all prayers bland and identical to each other, preventing you from standing out and being rewarded. Never mind the trust you would have to put into the priests to make sure they would actually say what they're supposed to!
More importantly from the gods' perspective, not understanding us would mean they would not know when they're being insulted and when they're supposed to smite mortals down! Can you imagine the horror?
Fun idea to have the gods keep language the same out of their own interest. Why should they use their precious immortal lives to learn languages!
Exactly! All those baby mortals constantly wanting to invent new ridiculous words to sound cool! XD