I moderate a reddit community with ~200k users, and if I didn't use strict filtering along with a slew of Automoderator rules I'd spend half of my day removing spam, shitposts, and submissions that break our posting rules. A few posts a day get caught by mistake, but it's a lot easier to free those posts than it is to remove the dozens of bad ones that would have made it through otherwise. I think it's at least plausible that the same type of thing happens at a site-wide level.