Because the vibe coded stuff is sometimes great, sometimes it breaks stuff, sometimes it breaks things that we fixed multiple times earlier. The PRs are too large, nobody can review that mess and you better be on call for your deployment. Maybe it will get better, maybe not. I dont know yet.
Oh, it won't get any better. LLMs already trained on every bit of code ever published, they won't get any more material.
The massive PRs is something that probably has to end. You can ai generate smaller changes in reviewable PR sizes. It probably even helps the AI code review tools to break the work in to smaller logical chunks too.