Despite the intentions of such a change, research into CTE shows that concussions, while extremely dangerous, are not the primary culprit of brain injuries in most of these players. Thousands of sub-concussive impacts, the kind you receive on almost every play, are the impacts that led to CTE.
It's like radiation. Yes, a large dose can be lethal, but health physicists determined that there is no safe minimum level of radiation exposure. Any exposure increases potential health risks.
The fact of the matter is that football cannot be played in a way that current neurologists would determine as safe and retain its core characteristics. Thus, fans and players will either have to accept the danger implicit in the game, or do and follow something else.