The part I don't understand is why can't they wait for the efficiency gains to materialize before firing people? Better pay a few people for a few months extra than be wrong. If AI is going to bring in all this efficiency, this would be peanuts.

Because, for white collar jobs, that is so rare that it's reasonable to say that it never happens.

Its like the "throw him into the deep end" method of teaching kids to swim. (I don't endorse it, but it has worked for many people.)