I believe the NFL has an agreement that they won't play on Friday nights so as not to interfere with high school football games. It wouldn't be bad late in the year however, when the high school season is over.
Yeah, I think one of the only stipulations that the NFL was held to in order to claim tax exempt status was that they had to agree to not hold games on Friday or the any Saturdays until December. That may not still hold true, but the fact that they haven't tried this makes me think it is. I feel like the NFL always presents this as how they like "to keep Fridays for high school football" when it is actually about the only thing they have to do to remain tax exempt.
The NFL can do whatever it wants right now because of its status but the decisions they are making are going to devalue their product down the road. The concussion issue is going to stick with people and it is going to harder for some to watch the games as the data continues to come out. On the other side, just as many are likely to lose some interest because the of the rule changes to reduce concussions. The NFL is different now than even five years ago (there is a reason why passing records will continue to get shattered and RBs are becoming more and more devalued).
Yet, even with this major issue, the league is floating ideas like increasing to 18 games, more Thursday night games, expanding the playoffs (does anyone want this by the way? It gets turned down every five fricking years; six teams and two byes per conference works well). Again, not going to hurt in the short term but these are bad decisions.