Where'd you see/hear that? It hasn't been my experience at least - but maybe I've just been lucky or undercounting the sites.

There are required steps to follow but none are "have x users" or "see a lot of spam". It's mostly "follow proper DNS steps and guidelines in the given format" with a little "show you're doing this for the intended reason rather than to circumvent something the PSL is not meant for/for something the public can't get to anyways" (e.g. tricking rate limits, internal only or single user personal sites) added on top.