Because he played it for a few snaps last year before he was hurt apparently. He knocked jones out at the goal line.. Then a injury.
That play showed how Cox can react to a play and get outside using his quickness and speed. I know he is not a MLB but LVE is slow reacting and slow running, a bad combination. Cox showed the ability to see the play and get to the ball in a hurry.
btw, wasn't Parson's supposed to be a MLB? To get him involved in the pass rush all the time now they moved him up almost like a DE. That puts a lot of pressure on LVE and he is just not quick enough for what they are asking him to do.
I also think Barr has lost a step too and has some similar problems to LVE.
If you want to know what is wrong with the run defense, just look at who the RBs are running past when they head down field.