Well.... it's complicated. I think the reason most girls get into porn is first because they're curious, they're open minded sexually, and getting paid to do something they enjoy sounds like a hell of a time. But once you start actually doing porn, you eventually realize that in many cases, it's more work than fun and play.
But that's not what I was saying in my previous post. I was saying that girls have limitations in porn because they're not comfortable with those things, not because those things don't pay enough. For example, many girls won't do anything involving pain, anything involving feces (so no golden showers and no two girls one cup), etc. They choose not to do those things because they aren't personally comfortable with them. Not because of the pay. It's like any job. Would you apply for a job that you weren't comfortable doing? For example, a person deathly afraid of spiders isn't going to apply for a job involving finding and selling tarantulas. And a person deathly afraid of heights isn't going to apply for a job working hot air balloons.
Anal is a personal choice. For many women, anal is a no-go, period, because it can be excruciatingly painful or, for some girls, they simply think it's nasty. When a girl goes to first work in the porn business and is discussing details with the people hiring her, one of the very first things discussed is limitations. There is a very long list: g/g, b/g, bbg, ggb, anal, fisting, toys, blow jobs, double anal, tit fucking, voyeurism, swallowing, deep throat, double vaginal, double penetration in general, bondage and other forms of bdsm, spanking, and many more. If a girl isn't comfortable with something, she simply says no.
It's really not that hard of a concept to understand.