Selling sexual services is a "challenging" activity.
It is risky, even with whatever safeguards you try to out in place.
It is in direct opposition with our instinct to have sex with people we are attracted to (if a prostitute only had sex with people they were attracted to, they would be unlikely to make enough money to make it worthwhile) ..
and/or have feelings for .. while people may have casual sex with essentially strangers, for the most part the human habit is for sex to take place in the context of relationships of some form or another - with familiarity, attachment, comfort, some level of trust, security, emotion etc.
It raises issues of privacy, exposure, judgement - people doing it are judged, gossiped about, seen differently, their families are affected; it is still seen as shameful (same as porn for example). You will find it extremely hard to ever escape the label/stigma if people come to know about it. Your kids will take flack for it, even if they're born after you stopped .. the go-to insult those who know from gossip will be ,"your mum is/was a hooker, whore, whatever".
If you're honest about it, it will affect your prospective partner opportunities. Most men are not ok with being in a relationship with a prostitute or even former prostitute.
Religions around the world still have a massive grip and it's not exactly approved of in most major religions. In fact it is thought Christianity made a female disciple into a "whore" to neutralise and degrade her. Most women with any religious leanings/upbringing will not be able to happily square it with working as a prostitute.
It can be painful - depending on the activity, man, frequency etc. It's not normal circumstances, with foreplay and relaxation with a familiar, loved partner.
All this and more ... Mean it's a very difficult "choice" and not a choice the majority of women will willingly make (if they have any real options). So the majority of women in sex work seem to tend to be those whose choices are curtailed or directed by negative factors.