Very good points in your replies!
> Imagine if tomorrow, Russia went on the defensive and froze its lines in Ukraine, setting up Surovikin lines everywhere,then withdrew half the forces it has currently committed.
They'd have to give up a big chunk of the occupied land to do that, since creating that line within 50 km of the front line would now be much harder than it was 3 years ago. Who knows, maybe that's what's stopping them from attacking another country as you described.