Why the fuck Russia should escalate conflict? In order to do what? Start a WWIII? This is not the russian goal. Nobody wants WWIII. Or maybe some of you guys? Anyone? No?
Nobody wanted what WW1 turned out to be, either. When people predict WW3, it's not a prediction of scheming masterminds bringing down the world, it's a prediction of somebody getting overconfident or making a mistake or otherwise taking a gamble that doesn't pay off. We had a Cold War for a reason, although I'm not saying you can equate modern-day Russia with the Soviet Union in all ways - just that you can equate nearly
any nuclear-armed state with the Soviet Union for the purposes of predicting the efficacy of military deterrence.
Saying WW3 is impossible is disturbingly similar to some advice that came up during the Cuban Missile Crisis: No rational person would choose nuclear war. Therefore, there could be no possible response to an attack by a nation armed with nuclear weapons. Therefore, the best option for the US to resolve a diplomatic problem was to
bomb the shit out of it. Hopefully, it's obvious why that's insane. Basically, it's not a realistic strategy to assume that nobody will choose an option that no rational actor would choose - there are a lot of reasons why, and I highly recommend studying this stuff for a better explanation than I can ever give over a forum, but things can happen that nobody wants. Game theory's a good place to start, although it tends to have the troublesome assumption that everyone involved is rational. Again, bringing up the Soviet Union is kind of a coincidence, since this thinking kind of applies to everyone, but here we are.
I don't know the politics well enough to say how likely some kind of WW3 scenario actually is to spring from Russian actions, but I know enough about human nature to say you should
never rule something out because it's too terrible to contemplate.