I think it's no accident at all that every popular porn-lady is a really slutty girl. Porn-ladies need to cultivate their slut image among porn-fans. Or else, they won't get many fans, and they won't succeed in porn.
The big problem that every porn-lady needs to solve is that she is always with some other guy, when you are watching her. The lady being with another guy usually means that she is taken and not available for you too. So, you aren't supposed to fall for her, fantasize about her, or become her fan. These are the normal social rules that everybody knows and follows.
There is only one exception to these social rules. Which is slut. When the lady is a real slut, then her being with another guy is no reason at all why you shouldn't also fall for the girl. A real slut doesn't belong to any guy. She is free to do it with any and every guy, including you too.
So, porn-ladies need to make themselves this slut exception. Or else, normal social rules apply. And them being with another guy in their scene is a turn-off for potential fans.
And that's where anal comes in. Anal used to be such a big taboo, that only real sluts would do it too. And even now, it's something only experienced, well-prepared, and well-practiced ladies will do.
Pussy-sex has a double meaning. It can be love, romance, and reproduction. Or it can simply be for pleasure and fun. But anal has no such double meaning. Anal is sex divorced from reproduction. The purpose of anal is pleasure and fun. Which is the purpose and the aim of every slut and every guy who wants to nail her sexy butt.
When a hot porn-lady spreads her cheeks for anal dicks, then she automatically breaks the normal social rules and makes herself the slut exception. Which makes it is easy for her fans to follow her, fantasize about her, and admire her sexy buns.
Ass and anal is the thing that does it. And of course, the lady taking on two or more guys at the same time also makes her the slut exception. Because when the lady is with multiple guys, then she obviously doesn't belong to any of them.
That's why one-on-one anal isn't quite as hot as when the lady does anal with two or more guys. One-on-one anal is divorced from reproduction. But it still might be a kind of anal love and romance, where the lady is committed to the guy. So, to eliminate this possibility, the lady needs to do anal with two or more guys. Or else, there is still some doubt about whether she is a slut or not. Which makes it hard for fans to fantasize about her.
When the hot lady is with you, then you want her to be faithful to you. But when the hot lady is with another guy, then you want her to be such a slut, that she is ready and available for you too. And in porn, the hot lady is always with another guy.
This is why so many porn-fans want to see hot porn-ladies take anal guys between their sexy buns. And one guy is not enough. They want to see multiple dicks between her cheeks. The lady needs to be a real slut. Or else, it's hard for porn-fans to fantasize about her.