It's absolutely possible to use an LLM to generate code, carefully review, iterate and test it and produce something that works and is maintainable.

The vast majority of of LLM generated code that gets submitted in PRs on public GitHub projects is not that - see the examples they gave.

Reviewing all of that code on its merits alone in order to dismiss it would take an inordinate amount of time and effort that would be much better spent improving the project. The alternative is a blanket LLM generated code ban, which is a lot less effort to enforce because it doesn't involve needing to read piles and piles of nonsense.