People using AI push a lot more code in a shorter amount of time. That deluge makes it much more likely for bad code, intentional or not, to slip by.

"Just leave it to a few trusted devs"

Some bad actors can play the long game. The XZ Utils backdoor is a very recent example of a contributor trying to abuse a backdoor he put there himself, after 2 years of posing as a helpful person.

"Let AI review it"

If humans are prone to mistakes, why would anyone leave a probabilistic program that is known to make bad decisions at random and that has, on more than one occasion, "cheated" to pass quality tests, deleted files it shouldn't and is still suceptible to prompt attacks, review it?

I understand the sentiment of "if the AI generated code is good, allow it", but the "productivity" gains in writing code means that, sooner or later, the person using the AI will care less and less about reading and preemptively catching possible errors because there'll be so many alterations that he either has to spend a month reading, or just skim over and accept.