how the hell is this guy not getting suspended for 10+ games at this point?
Good question.
In the thread on the Stanley Cup forum there's the usual lamenting about how the sport has gone soft if people want suspensions for this sort of thing. The league has gone soft, but in a different way. I grew up watching the Dead Wings. If Marchand had done that to a Wings player Probert would have destroyed him. And I don't just mean in a "square off drop the gloves" fight. He would've gone through whatever linesman or teammates were going to protect the Rat. If he felt like he didn't extract his pound of flesh, then Probert might do something like run the goalie next time he goes out to play the puck, creating an all out line brawl and more opportunities for justice.
But that's not how the NHL operates anymore so we're in this middle ground where there's enough old school guys in the front office who look at Marchand's cheapshot as playoff hockey or gamesmanship, but at the same time the rules have evolved enough to protect him from a proper beatdown. The league doesn't punish him and there's no way for players to really punish him so rats like Marchand thrive.
What other legitimate sport hands out zero punishment when one of its players approaches an opponent from behind and punches them in the back of his head while he's down on his knees, after the whistle, near the end of the game, especially when he waited until the refs weren't looking?