Plus, Russia is already attacking Europe and has been for a long time, except not militarily but electronically, politically and economically: gas distribution disruption, cyber attacks, intervening in elections, lobbying for fossil fuels and right wing parties, weaponizing migrants at EU borders, etc.
That's the kind of warfare Russia does in Europe and it's more effective than sending things that go boom as those can more easily be countered. Political destabilization is more difficult to counter.