Facebook has a history of letting crime groups operate even if they are obvious and don't even try to avoid detection: https://krebsonsecurity.com/2019/04/a-year-later-cybercrime-...

Is it really surprising though? Criminals, including pimps and child rapists, still watch ads, "engage" with the platform and increase the user numbers, and even encourage their peers to also join/engage with the platform. For something like Facebook surely it's a no-brainer to not miss out on all this "engagement".