I listened to a retired head ref (who refereed several superbowls) on Mike & Mike weigh in on both the non-PI call & the Dez non-call. I tend to agree with him on the non-PI call: after watching the play live, I could tell that it was NOT DPI, because the DB had both hands off the WR, but the WR had both of his hands grabbing the DB! i.e., he wasn't try to catch the ball, he was falling backwards grabbing the DB & trying to generate a DPI flag (a la Odell grabbing Tree's facemask on his way out of bounds to draw a late hit flag). I was yelling at the TV when the flag was thrown, just to make sure the ref heard me
Also, per the old ref guy, the WR has to be making an attempt to catch the ball for it to be DPI. The ball wasn't catchable anyway, hitting the DB in the back.
Also, according to the retired ref guy, it was not the line judge who threw the flag, but another guy down field; the line judge, who was closest, disagreed with the flag, but did not communicate it to the head ref on the field on time before the head ref announced it. After he told the head ref it was not a foul, his call overruled the other ref's call, so the head ref picked it up--extraordinary, but still within his right to do so if he believes the call needs to be changed.
As far as Dez goes, players on the sidelines enter the field OFTEN during games; refs usually give the players a bit of lee-way to get off of the field before they throw an Unsportsmanlike flag. I didn't see Dez, but according to the retired ref guy, Dez got off the field quickly, and it's the ref's prerogative to throw or not throw the flag. Usually they throw the flag only if the player keeps getting in their face & doesn't leave them alone.
I'm not saying the NFL is not fixed, that's a whole other ball of ear wax.