AI reviews are flaky - maybe correct 80% of the time - and everyone hates flakiness.
AI code reviews easily double the work in reviewing: you have to both review the original code and the AI code review. The AI code review can be 80% correct, but you never know which 80% is correct and which 20% is garbage, so you have to review all the AI's comments.
Maybe but I'll take a 80% correct review over no review at all. If it alleviates a good chunk of back and forth between the reviewer and the committer, it's still overall a time save for the maintainer.