Haven't watched them, but a forum for predators would be fairly easy to shut down just by baiting various people into doing things like propositioning what they (the predators) think are minors, sending in anonymous tips and reporting the inevitable CSAM a forum like that would share, etc.
Start from the top (highest mods), go to the bottom. Here doesn't exactly work like that. First of all, the population of people here who do illegal things isn't... particularly dense?
Sure some things people buy for CTB are tentatively non-legal, but so is testosterone that cis men use to dope, or the DIY HRT community that has existed for years in transgender history. Hell, most left-leaning low-income people have had to skirt the law in some way like that. It isn't really cracked down on that much.
As for actual illegal stuff, 4Chan would get shut down before we did if we're going by "amount of genuinely fucked up crimes."