If you see a PR and the guy is verified, you can check his name, his linkedin and where he works, at least there is some accountability if he introduces malicious code.
If the goal is to reduce slop, define slop. As a maintainer of a project you should be able to tell if something is slop.
If you don't have time to read PRs (which is the real issue here) that's fine too.
My guess is they want to reduce the amount of PRs, and ensure that the quality of the PRs passes an extremely high bar.
It's not an impossible problem, but it's a resource allocation problem, and they don't seem to have a way to address it at the moment besides closing all PRs.
Of course they can, the problem is they have to spend time digging through a ton of garbage looking for the ones that aren't low quality slop.
If you're getting DDOSed, you start by putting up a firewall lol.