I'm not sure they are, they're just not nearly as public. Kim Dotcom is / was notoriously boastful about his actions, and all the money he made off those actions. I've never heard similar things about the founders of any other file hosting service founder/owner that is well known for piracy. Makes him an incredibly appealing target I think.
Same as PirateBay, which made its name when they publicly replied to copyright enforcement letters with insults. Refusing to be humbled by established authorities is the real crime, because it corrodes their legitimacy and hence their whole existence.
It's a bit like being homosexual in countries with harsh state-religions but tolerant attitudes: keep it quiet and nobody will bother you, but if you flaunt it then the law will crack down on you, because you're attacking the basis of the whole legal edifice.
