And here's why......
By repeatedly pausing and playing this video in slow motion you can clearly see that CB Jacques Reeves reads the run and is unblocked as Johnson takes control of the ball. However, instead of attempting to break up the play in the backfield (7 second mark), Reeves turns his back to the ballcarrier and begins to take the perfect angle to make the tackle 33 yards downfield.
This is just another case of the game showing it's age and being exposed for having--what is in my opinion--unacceptable AI.