I have a theory: The camerawork/cinematography is better.

Historically, there’s been a divide between softcore and hardcore porn. Softcore porn generally features R or NC-17 rated nudity and some simulated sex acts with a lot of effort put into the cinematography to make sure the camera never goes crotchwards. These kinda rely on a suspension of disbelief, often bolstered with more of a story focus, some are basically soap operas.

Hardcore porn on the other hand features genuine non-simulated sex acts by definition, and the producers seem to have an attitude of “if we’re going through the trouble to have real sex in our movies, by god’s cock ring we’re going to SHOW real sex in our movies.” So the camera ends up at all kinds of stupid angles - way low looking up, titled to one side to better fit tall humans onto the wide frame, or downright gynecological close-ups that go on for minutes at a time.

The step-sibling genre on the other hand…these usually do feature genuine sex acts, but they’re playing to a kink that…isn’t visual. The aspect that makes this not a vanilla movie is the actress occasionally remembers to say the words “I can’t believe I’m fucking my step-brother.” So that pressure to zoom way into the crotchal region seems to be relieved. The camera stays upright at eye level across the room. Close-ups are few and far between or totally absent; the actors probably do that thing where they lean to the side to “show their work” but we don’t plunge in to get a good look at the wrinkles and razor burn. So what ends up on the screen is two people having sex rather than a penis going into various holes.