Just to throw more ideas out:
The cinematics suggest the mind flayers are dying. There were already many mind flayers who were dying before the attack and crash. Perhaps the tadpoles is their last ditch effort to survive as a species?
That may require godlike power. And we know in Faerun, the number of worshippers increase the strength of a god. Maybe the mind flayers are trying to elevate their own god through tadpoles. Mortals have ascended to godhood in Faerun.
