Sometimes the Camera man is the owner. Sometimes not. Maybe he got into the hassle and work of porn to get more out of it than just being a wrist monkey holding a camera.
Sometimes the director is trying to "break down the wall". The conceit behind so much porn that gives us some completely artificial situation and pretends its not completely artificial. (Locker room??? That's a stretch.) So the director is like, 'Why pretend?'
Sometimes it is to please the audience. Some of the audience, anyway. Put a 'real' guy into the fantasy for all those potential guys out there who may not be as attractive as your average porn hunk, but would like to believe someone like them -at least in fantasy- can 'get some' too.
Sometimes the camera man is just an average guy, but (in the eyes of some... perhaps to even the performing model) is hot enough to be in the shot. In the eyes of some. There have probably been zillions of shoots where one model wishes he were paired with the camera man vs. the model he's scheduled to shoot with.
Those are the best reasons I can come up with on short notice. None of these answers probably make you feel any better about the vids you've seen. We like what we like. We don't like what we don't like.
The great news is, if -by chance- you're annoyed there's some 50 year old guy hanging out in your porn, you'll probably feel a lot better about it when you're 52.
Things to look forward to.