College aged adults aren't immune to the long term effects of repeated head trauma. Unreported injuries among younger players may even be worse because of lying to stay in the game or trying to go all out to get noticed and win that lottery so many poor, talented kids buy into. But you don't see what happens after the years of them hurting themselves; no one follows and reports on the has beens who never made it, the ones who failed on the road the stardom.
Football is dangerous to long term brain health as long as people are impacting at any force with their heads and spines. There's more to the game than brute collisions and take downs, but it needs a rules update for it to be on the right side of modern medical science in the 21st century.
The only reasons not to are to protect the feelings of everyone who's been rooting on the pain and to shield the heads (how funny) from liability and litigation against their investments. If they admit the way it's being played hurts people and damages their brains, it'll be a shitstorm of guilt and blame. Parents, coaches, and fans all over are going to blame themselves for pushing their and other people's kids into getting late life brain damage for some local fame and and viewing pleasure.
Right now, someone is running damage control in the news saying reported concussions are higher for every sport compared to football-- emphasis on reported. No one is writing it down because it's just a "part of the game" unless they get knocked out or seize and EMS is called. If you're still on your feet and a smelling salt[1] gets your eyes focused, you're not concussed, you just need to toughen up. I wish I were exaggerating.
[1] http://webcache.googleusercontent.com/search?q=cache:6_QhPICfavwJ:escholarship.org/uc/item/7qq7b12k.pdf+&cd=1&hl=en&ct=clnk&gl=us