I think the difference is with porn sites the actors have signed contracts and gone through several legal requirements to ensure a "safe" enviorment. They also generally don't do the more extreme porn fetishes that are illegal in some countries (Think rape/incest roleplay. But the list is massive.)

Onlyfans and sites similar often attract the small fetish sex workers because the demand isn't big enough for a major company to pick up on them on a regular basis but the demand is enough they can make serious money freelancing.