Mostly because most spam isn't going to be reported. Traditional anti-spam works because once you have a handful of reports, you can probably generalize it to an entire class of spammy pages generated using a particular technique, and get rid of everything.
LLM-generated content is not distinguishable from human content by any simple rule, so you lose the ability to police the platform that way.
LLM-generated content is not distinguishable from human content by any simple rule, so you lose the ability to police the platform that way.