Attractive and physically desirable women were assumed to be readily available to influential and powerful men for sex. And if one lady would not, then others would be only too keen and instantly available. Yes Grace Kelly married her Prince, but only after she was introduced to him by a powerful studio head looking to curry favour. And “her” Prince had explicitly come to Hollywood looking for a world class beauty. In those days his behaviour was called being a play boy. Hers was called being lucky. No-one would have thought to call Grace Kelly a courtesan, floozy or hooker.
In the same way, Marilyn was perfectly content to use her physical sex appeal as a tool for both her advancement and for her pleasure. She had an extremely lengthy list of lovers and one-night stands, most of whom were in the movie or acting industries. She used her body, sex appeal and sexual talents to get her the work. Until she was a big enough star and had enough power of her own that she could afford to say no. Though, to be honest the Kennedy brothers found that she did not actually do so all that often.