You're not wrong, however the issue is that it's not always easy to detect if a PR includes proof that the change works. It requires that the reviewer interrupts what they're doing, switch context completely and look at the PR.
If you consider that reviewer bandwidth is very limited in most projects AND that the volume of low-effort-AI-assisted PR has grown incredibly over the past year, now we have a spam problem.
Some of my engineers refuse to review a patch if they detect that it's AI-assisted. They're wrong, but I understand their pain.
I don't think we're talking about merely "AI-assisted" PRs here. We're talking about PRs where the submitter has not read the code, doesn't understand it, and can't be bothered to describe what they did and why.
As a reviewer with limited bandwidth, I really don't see why I should spend any effort on those.