Porn creates and distorts scenarios for entertainment purposes. It’s fiction. There’s no point comparing our bodies, sexual preferences or expectations to fiction, whether it’s porn, a Hollywood romcom, or a novel about sexy robots.
The actors in porn are often cast because their vulvas might look a certain way, or they will alter their vulvas to achieve the same look. Why is this look the norm in porn, you ask? There are lots of reasons, and none of them have anything to do with the real world (waxing, for example, exposes every intimate detail of the vulva to the camera).