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.
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.