I can't help but feel that "they broke the rules!" is a hollow argument in a case like this. Most obviously, because it's not clear they
did - Vroom's contract didn't prohibit ticket sales, but that was still the grounds for revocation.
More broadly, though, the issue of selective enforcement is a thorny one. If you write a contract sufficiently byzantine and ambiguous, any legitimate use will rub up against the edge of some prohibited behavior. At that point you have a totally broken agreement - you preserve it for anyone whose behavior you like, and revoke it for anyone who crosses you.
It's like the issue of selective policing. We live in a world where "don't commit any rules" isn't a viable answer, because there are endless lists of ambiguously defined rules on everyday tasks like accessing a computer. So if someone decides they truly want to pursue you, they can dig up a website where you mis-entered your birthday, declare it fraudulent misrepresentation, and try to put you in prison.
If everyone is guilty, the only question is how you decide what to pursue. And in this case, it's painfully clear that American didn't pursue egregious violations or frequent offenders, they went after anyone who had taken advantage of a product they regretted selling.