Well, it's. A bunch of things. The players have gotten massively bigger with steroids and scientific body building. So instead of two 160lb guys whacking each other like in the 1920s it's two 300lb guys. Helmets and pads let people hit each other real, real hard without ijury to the body, so they're getting hit more often, so they've got more chances for tbis. Tbis result from anything that knocks your brain around, not necessarily things that cause concussion. They build up over time, causing more and more damage.

And this is just subjective, but people seem a lot more vindictive now, hitting people harder when there's no need.

We had this problem in a larp. Headshots were illegal, but even accidental blows to the head could add up so we were really encouraging people to start wearing helmets and head protection.