the reason you tend to see many of the same guys over and over in porn is because they can "perform" in front of the camera. Many guys think they can, but when the big moment comes they cannot even get it half-way up. It is not as easy as you think to fuck on cue in front of 10 strangers, while lighting and sound guys are walking around, director is giving instructions, people are sticking cameras and mikes inches from your ass, etc. At least this is what I saw on a show about the porn industry.