The inconsistency of the NFL

The highlight of Thanksgiving night was the rivalry matchup between the Pittsburgh Steelers and Baltimore Ravens. The last few minutes of the game were incredibly packed with excitement and action, but also included a scary moment, when Pittsburgh running back Le'veon Bells suffered a vicious hit to the head by a Raven defender. By NFL rule, the play is called dead the instant the ball carrier's helmet is knocked off, which happened just shy of the goal line. This was a second-down running play in which Pittsburgh needed a touchdown and 2-point conversion to tie the game, and the ball was spotted inside the one-yard line for third down. You can watch a video of the hit at this link, scrolling down to the first of two videos. I don't have a problem with the rule of the play being blown dead with the coming off of a helmet. My problem is the fact that this was a direct helmet-to-helmet hit and absolutely nothing was made of it. In the lone night game on Thanksgiving, in the closing stages of the game, when the announcer calls it a helmet-to-helmet hit, there has to be a penalty called. Especially if it knocks a helmet off and renders the running back borderline unconscious. I'm not going to bash the NFL, but it would be pretty easy to do so. I just wanted to share my thoughts on a non-call that completely contradicts the NFL rulebook. But hey, would it be the NFL if this kind of thing went the way it was supposed to?