The culprit is this whole 'game management' kick the officials have been on for about a decade now.
They seek to line up penalties - 'oh we called three penalties on team A and none on team B, so we need to give the next two penalties to team B!'
Instead of just calling stuff as it happens, the team be damned.
Both teams got away with stuff; some Habs D held Marner's stick for like five seconds at the beginning of the 2nd and Rielly was bleeding from a high stick when he scored. Danault got sticked in the face, but he was down on a knee during and so it wasn't really a 'high stick'.
Interference? If interference was called in the true spirit of the rules there'd be an interference penalty every two minutes, slashing same.
Call this shit as it happens, stop trying to make sure each team has the same amount of power plays a game.