[atmanthedog]

A lot of comments here talk about the defense padding, and that's certainly part of it when it comes to long-term, low level concussive hits to the head. The idea is also mentioned in other comments that the problem is not sufficiently realized in rugby: that is also probably true.

There are also other factors. The forward pass often puts receivers in dangerous positions, as they often have to turn and track the ball when it isn't thrown perfectly. Also, the stop and start nature combined with the spread in position that the threat of the forward pass creates more high speed head-on collisions. Extreme specialization among the positions also mean that there are a lot of very large, very fast people out there whose job is just to hit as hard as possible.

Those game mechanics also combine negatively with the amount of money at stake due to the extreme commercialization. A lot of these players grew up in high school or younger programs being told that if they want to go pro and make the big money, they have to be out there hitting the hardest, or there's always someone to take their spot. That isn't really incorrect, but it leads to poor outcomes.