Crows have only been around in one form or another for 30 million years give or take, so if they haven't done anything more interesting than adapt to their environment and use basic tools since, I don't think it is unreasonable to assume that the reason is because they are incapable of it, not because they have chosen not to.

At the end of the day, it is impossible to prove a negative, so no I can't show you off hand that a crow can't actually conceive of this or that or the other thing