Because females -- for a certain number of years -- have a body that is very good at serving as a sex doll. Many cultures allow some of their females to "sell" this aspect of themselves, and some females are capable of doing this type of "work" just as some people can work as butchers or do other "unseemly" jobs. If prostitution was legal in the U.S, a lot of women would do it. Aging wives and women who want a maximum return on their quality as bio-sex dolls maintain (with their votes) a prohibitionist prostitution regime out of self-interest. It's like a hockey league adopting a helmet rule which disadvantages everyone for the greater good (safety) of all. Women banned prostitution to maximize the return they could get for their quality as organic sex dolls in terms of marriage/support. The cost was the average woman could not work as a prostitute if she wanted. Well, with the decline of monogamous norms, now a greater ask is being made of the average woman in demanding that she doesn't take advantage of her bio-sex-doll quality to earn easy money from the many desperate men. A conflict between women who are willing to work as whores and therefore "betray the sisterhood" and the more traditionalist women who resent them is quietly playing out in U.S politics.
