I think they would work fine if the surveillance and advertising industry were overnight christened criminal enterprises and users had to start paying for what was once '''free''' (cost of entry: pieces of your soul, bit by bit).

Decentralized has a small convenience cost and the crime of surveilling everyone to advertise to them (among other uses) is too cheap for decentralized to come out on top. Note I am Atheist when I say this: if law doesn't hammer the scourge, those who get religious about this stuff are the ones who'll enjoy any modicum of sovereignty.