Do you think a lot of amateur porn is people who have been kidnapped, or are being blackmailed, etc.? It's the only way I can explain why someone would do something sexual on film, knowing those images will be floating out there forever. We're talking about thousands of people, all over the world (and some of those "teens" are obviously not yet 18).
If you ever plan on remaining legitimately employed, why on earth would you show your ass (and face) on camera?
I like to imagine they are being held captive and forced to do porn under threats of death and promises of meth.
It makes it so much hotter.
The kind of porn that's used with models procured via sex trafficking is the kind with an underground following (e.g., kiddie porn, snuff films, raped/unconscious victims, etc.). The mass market stuff generally features people who are dirt poor or have low self esteem. Charismatic pornographers will prey on them by throwing around money and compliments, and then they'll make it seem like the model has a choice ("Even though I spent all this money on you and treated you special, you don't have do do anything you don't want to!").
To seal the deal, a lot of models are promised that the pornographic content that's produced will only be sold in markets abroad (European companies use this one). Companies like Sean Cody and Corbin Fisher scout for amateur talent, fly them out, pick them up in limos, and take them to nice restaurants before taking fairly innocent beefcake shots. Barebacking and higher earning opportunities are offered once the waters are tested...