In their mind Piracy might kinda maybe theoretically sorta be a lost sale, but keys bought with stolen credit cards literally cost them money because of the fees from all the middleman payment providers. So not only does their bank account not go up, it goes down.
Even if it didn't cost them money, it would be purely enraging to meet someone who is making money on your hard work for nothing at all. Just pure parasitism.
Many piracy sites run ads though, don't they? Unless everyone visiting runs ad blockers (unlikely) the people running those are making at least some money. Presumably it at least covers the cost of running the sites.
It's probably just as the comment you replied to said: "stuff bought with stolen credit cards (and resold on those sites) actually costs us money, as opposed to piracy which merely 'costs' us money".