Basically only fans was started by actual celebs as a bit of a way to contact them and get behind scenes pics and videos , proper fan girl site so to speak. Cardi b has one and I think Katy Perry used too before it got sexualised . People can post what they like but it’s had a massive boom in the adult industry and with instagram deleting sexual posts they have dived on it .with only fans you post what you want too , not what you’re pressured too . It works like a strip club type thing , the subscription is your entrance in and the pay per view pics are your private dances lol that’s the easiest way to explain it