Why no challenge on the Gurley play that should have been a TD?

In the 3rd quarter the Rams kicked a field goal to make it 27-13. However a couple plays before Gurley appeared to run the ball in for a score. He went low and dived into the endzone, breaking the plane with the ball. They side office ruled him down but the replay clearly showed he had broken the plane of the goal line with the ball. No challenge? Why? Could it be because McVay was down by the pilon on the far side of the field with no headset on nobody could tell him to challenge the call?

Grits