Broken noses, cauliflower ears, missing teeth and lacerated scalps are just nature's way of letting you know that your noggin is taking a beating, and that you should do something protect it. Modern protective equipment greatly lessons all of those injuries, and thus lessons nature's signals. But modern protective equipment does not keep your brain from bouncing around inside your skull when you get hit, or hit someone, hard enough.
Sammy Baugh was whip smart at 80. Many modern players are mumbling and shaking in their 50s.
The game was played on grass. Astroturf and other types of turf cause most of the concussions.