There are particular rules about hitting the quarterback, and in this session in particular a crack down on either landing on the quarterback with your body weight, or lifting and driving them into the turf.
In this case, although Matthews body and head are to the side, you cans from one angle after he contacts the QB he lifts the QB leg and then drives him to the turf and does land forcefully with some of his bodyweight on the QB, exactly what they are trying to stamp out to minimise injury to marquee players who lets face art create much of the excitement in the game (I stopped watching the Packers last year after Rogers was injured as they were just plain boring to watch).
I'd rather a few borderline over zealous penalties than injured QBs.
Other hits you mention are allowed in certain circumstances to certain players. There are rules about defenceless receivers getting gregarious hits, particularly from the blind side where they do have have the opportunity to brace. And remember the outfield players are generally bigger, stronger and much better protected and able to take such impacts. You rarely see an injury from a tackle in the air, whereas there are loads in the offensive/defensive lines from players falling at awkward angles.
