Bundle operators and game developers engage with consumers on the grounds that the keys won't be resold individually. However, they have no way to control this. So they make reseller/G2A responsible for complying with terms of an unenforceable honor code. Seems a little arbitrary to me. It's akin to a grocery asking you not to sell eggs individually from a carton you just bought from them. (How are they gonna enforce it?... And as a consumer, are you even OK with not having full control over what is now your property?)
I think this is a problem with the business model, rather than the problem with "unethical" resellers. So you either give up on the business model, as many game devs are doing, or you find ways to enforce it. Either start suing users who resell keys, or partner with the likes of Steam to create a system in which keys can't be activated individually.