Two words -- honor code. Rock the boat and you will find yourself in an unpleasant situation, so instead everybody does good work and nobody asks too many questions.
Honor codes for stuff that traditionally involve corporations going after individuals for criminal charges. I feel that's a bit of a crazy proposition.
When people say "honor code" around me, it usually means, "Do something honorable, even though it's against your self interest."
For both white hats and Pornhub, the legal/authorized bounty system is in their interest. White hats are making less money than some black hats, but they're not constantly terrified of being prosecuted under intense anti-hacking laws. Pornhub is spending a lot less than they would if they were hacked by black hats. Both parties win.