Plus, to some degree, the male and female minds are wired differently in terms of sex.
1) Some women think of masturbating as dirty or just something they don't do. Seriously, I know there is the perception that everybody resorts to it when they get sexually frustrated, but to some women they don't understand it and can't get their heads around the idea of making themselves sexually aroused when there is nobody else there. I actually went out with one of these women, and she said it would feel weird doing it herself. She ended up getting herself used to it by starting doing it with me watching, and there was no turning back. Not long later she confided in me that she'd bought a Rampant Rabbit for evenings we weren't together.... LOL. But yeah, there are still some women that think of self-love as a filthy, disgusting habit for monkeys. The term "self-*****" probably sums it up.
2) For guys to talk about jerking off in any respect no doubt sounds puerile or creepy/sleazy. They all know we all do it, but there are some things you don't talk about.
3) To tell a woman that you masturbate over her image comes across as a *********, you're objectifying them in a way they don't want to be. Like Harley says, it's all about context, it's about a comfort level that your normal woman outside the biz will rarely have. It almost becomes an issue of consent. Women in the industry are engaging in sexually provocative imagery that is usually designed to create arousal, so in a way they are consenting to becoming objects of sexual desire. Your woman in the street or next-door neighbour hasn't. My ex used to have a problem that I'd occasionally watch porn * for self-gratification because she so liked the idea of me masturbating thinking about her, but that's within established borders - she's already consented for me to use her image (and body) for my own pleasure. Again, that girl from work with the tight top hasn't. This why you don't stare too long or whistle in the streets ; it's objectifying without consent.
* Occasionally. LOL. That sure has changed.