I think the answer as to why now is simple enough, Putin knows his reign is nearly over and he wants to be able achieve his goals before he goes.
There is that, there is giving up on the West, there is being a part of Team China now, and there is that the Ukrainian's keep insisting upon poking Russia in the eye...a little of that goes a long ways.
There is also that we in the West have not behaved honorably with Russia, as China well understands.
There will be changes.