Supposedly there are almost 13m accounts on the site, I would expect at least some of the accounts which have uploaded personal content could be valuable for extortion. Even without having uploaded content a profile of someones porn habits could be used for blackmail.
People who are not aware of the risks, they also happen to be the most vulnerable targets (extortion for example).
I don't think these people were unable to use any other email address if they were paying members. Unless they linked their bank to their work email?
Quite the contrary. Imagine, as someone mentioned elsewhere in this thread I think, if the adtrackers got hacked. What might it reveal about you?
If someone threatened to email your boss your entire browsing history, how much would you pay to prevent that?
What if it was being sent to you wife? Your mother?
What if it were being broadcast to the world at large?
These hacks are a dime-a-dozen. Everyone sees Ashley Madison hacks or xHamster hacks and thinks, 'well that's not me. I don't go to those sites.' But it very well could be you. Or worse, someone could falsely claim it was you...
I am not aware, does xhamster require confirmation of the email address before using the account? That might also be a way to sign up using someone elses email.