You should watch the VICE documentary "Life Inside a Secret Chinese Bitcoin Mine".
I think the man they interview says that he sells some BTC to pay for costs, and he holds the rest because he thinks the price is going to rise.
Not all of them are evil
Thinks about the profits, not the actual concepts that bitcoin could actually bring. Given that most of the hashing power comes from China, there is no doubt that they only want the profits. If those mining farms formed together and centralize their mining power, I don't know whether I'll stay with bitcoin or not. If ever a big dump happens, then we might have some idea who did what.