I think it's a matter of volume, it's extremely easy and quick to publish large amounts of generated code, and by far most people won't go searching your codebase in depth to see if the code is decent, if it works as advertised they don't have a reason to look into it further. If you add a third party to vet all code then you're still giving massive amounts of work to whoever has to review the mountains of slop.

It's not like we didn't have an issue like this before, about people copy pasting without understanding anything, but these tools made it more accessible and streamlined, and the worst part is that vibe coders believe sharing their slop is of value.