lolz
They get paid to have sex.
No, they get paid to act like they are having sex for short cut scenes. It is far more complex than filming most film scenes because real sex is so imperfect and difficult to capture on film. The idea of porn is to create perfect, stylized images at exactly the right angles.
They film hundreds of these stylized clips for an entire day at the whim of the director. Multiple angles, constant reshoots, dozens of retakes of each position change, constant makeup and lighting issues, synchronizing audio, etc, etc, etc.
Then a few of the scenes get spliced into a single scene that looks like they are simply having sex. It looks easy, but in reality those 15 minutes of what looks like straight sex were spliced from an entire day of grueling short shots.