It's partly an honor system but also, anyone distributing malicious cracks are quickly called out whether its on public tracker comments like PirateBay or removed from private trackers.
Distributors of GOOD and CLEAN cracks often earn good rep in the community too, like Monkrus which I've had no issue with before.
Also, in my experience, installing a malware-packaged adobe app isn't actually all that bad if you run a malware scan immediately afterwards. With the scale and breadth of software piracy there isn't much money in making advanced malwares beyond bundling an existing one into an installer. I don't recommend it, but it's still easier and cheaper than paying Adobe!
TLDR the community polices itself pretty well considering.