Because Tiktok is from China. Youtube, Meta, and X are from innocent America, how can they foster such content!?! /s

Because none of the others you mentioned have anywhere near the same grasp on the attention of today's youth like TikTok does. Those are boomer platforms at this point, making there little avenue to direct children toward sex work because there's basically no children on the platform to begin with.

Not that they're not also problematic for a million other reasons - they absolutely are, just not for this particular reason.