great engineering effort was spent to make software at FAANG built on clear service oriented modular architectures, and thus easy to develop for. Add to that good organization of process where engineers spend most of their time doing actual dev work.

Enterprise software is different beast - large fragile [quasi]monoliths, good luck for [current] AI to make a meaningful fixes and/or feature development in it. And even if AI manages to speed up actual development multiple times, the impact would be still small as actual development takes relatively small share of overall work in enterprise software. Of course it will come here too, just somewhat later than at places like FAANG.