It seems like a lot of the most well-known pseudo-legal BitTorrent "groups" (PopcornTime, YIFY, ISOHunt, now Kat) turn out to be one-man shops, and as such, just completely dissolve as soon as their owner crosses paths with law enforcement. In some cases, these services are integral enough to the "scene" to be brought back by others. But other times, everything just stops for a while. This seems like a bus-factor pro…
I mean, I would assume it's because it's shady business. Even if you made it multi-national, there are probably only a few places where you could reasonably keep the server hidden for an extended period of time (Keep in mind, these aren't Tor services or anything, they're pretty out in the open as far as I can tell) - and you're making money off of ads, so actually getting paid is another complicated issue. And really, if you only need one person, why bring in the risks of a second one? I don't think you'd be very concerned about "keeping the scene alive" if you're going to jail.
Wikipedia is easy in comparison because most countries don't throw you in jail for running a Wikipedia server.