Either they like the Point Of View aspect of it. The way those 3 pics and video are shot, you can easily pretend you're the guy whos getting his cock sucked.
Most porn and in most positions (either when the guy is getting dome, or its missionary- doggystyle-whatever) Im putting myself in the guys shoes.
Im not sure if your ideas on porn is not to have a guy visible at all. Ive known a few men like that, mostly middle eastern men, who say they cannot handle seeing a man in porn and only watch lesbian or girls doing solo masturbation scenes. Ive usually gotten the vibe that they are secretly trying to fight their attraction to the male body and not having a guy in the porn scence helps them not hate themselves because they are end up jerking off to the man instead of the girl.