Regarding these artists.
I can't say what caused any one to stop posting, and close their accounts, but it often has little to do with censorship.
People get older, fall into work and family life, and time they once had for art they give away for free dwindles. Like any hobby the time comes out of their life, and other things always clamor for it. So they stop, and no new stuff appears. Rather then answer messages and so forth they close the account so it's not a distraction.
Other simply get annoyed by the endless shouts for MOAR!!!! and the true lack of real feedback they get, and start to feel like fetish wank material machines. So they saw "Screw it, this is not fun." and go away.
Others just burn out. They have said all they have to say and rather then recycle themselves they leave.
Just how it goes. Even the biggest stars fade. BAC and C.A.B. come to mind.
Myriads