In my mind, contact sports have become more and more dangerous with every generation. There is no single contributor but many working in parallel.  

For example, the quality of  protective equipment has reached a point where there are no consequences to self when a player makes contact. If you engage another athlete on the field, you will not suffer any pain when delivering a blow.

Athletes are also better trained , so collisions are much more violent today than even a decade ago.   

Saying all that, myopic coaches need to shoulder most of the blame.  Many  coaches are only there to win rather than develop character.  Thirty years ago, there were always mismatches between teams. However, a coach who had some level of  maturity would send in their 2nd stringers when playing weaker teams.  Got to wonder if the coach even thought of it.