DB rule #1, Deeper than the deepest. If you are, you can't get pushed in the back.
How many guys was he clustered around? That DB had no chance to get in the back of the end zone. And if Tate didn't blatantly cheat and give him a two hand push in the back that was worthy of whiplash, that DB would have been in the best position of all the players to make a play on the ball. That was the worst offensive pass interference I've ever seen that wasn't called, at least as far as I can recall. And given the circumstances just about every set of eyeballs was looking right there- it's mystifying how no offensive PI was called on that play.