well if the publishes/Steam whatever dont spot that as dodgy they only have themselves to blame.
Well, one time Ubisoft withdrew a big batch of stolen keys. This meant lots of people who had bought the game (but bought from dodgy key sites) suddenly had their games disappearing from Steam/Uplay.
Despite Ubisoft having been stolen from, the public relations fallout of withdrawing the keys, with the outcry from the buyers of those stolen goods, meant that Ubi wound up actually looking like the bad guys. They cut their losses and reinstated the keys.
All that said, My first post was a little black and white. Some (many?) of those cheap keys will be bought from cheaper territories, so the publisher gets some money rather than the £0 they get from the stolen ones.
I'd personally still buy AAA games from keysites, on the basis that they are more likely to be greymarket rather than stolen - more disparate regional pricing than for indies - and more able to swallow the loss if they are nicked. I wouldn't buy an Indie title from there, though.