I think the main reason you haven't seen a lot of changes on the surface is that corporations as currently constructed largely cannot use them efficiently.

I have a personal project where I am merging 100+ PRs a week and at work I would be lucky to merge 8. I spend 20x as much time trying to get PRs merged as I do actually doing the work.

I'm on a project with 4 other people working on 4 or 5 microservices and I would get more, better, work done if I were on a team alone managing all 4 or 5 microservices myself.

Yep, and we've known this since the Mythical Man Month, but the biggest slowdown is coordination overhead. However, if one person can do much more work, you need fewer people overall which means even lesser coordination between them, which is when broader organizational productivity gains will be unlocked.

So the answer to why we don't see AI productivity gains more broadly is, unfortunately, enough people have not been "re-orged" away.