That's a very good question i've thought about as well. I don't think the Kremlin has much use for him anymore tbh, but they aren't going to hand him over either without getting anything in return. He's too much of a PR gift.

> Because he does criticise the Russian government openly and often

He is careful in what he says, and makes sure not to question the levers of power Putin has (elections, policy state, etc.). I have no doubt he has been given clear guidelines of what to avoid saying, as he is living by the good graces of the Kremlin now.