The ones who can't are usually weeded out of the industry pretty quickly.
Ask any porn star what her least favorite position is, and I guarantee you that nine out of ten times, that answer will be Specifically the porno version, which is when the guy is on his back, and the girl is squatting on top of him facing his feet with her own feet planted on either side of him, like she's playing leapfrog on his penis.
In all seriousness, anal sex in porn requires a lot of planning.