Mostly, somebody with a hand injury ends up paying for the related experience themselves or (if 8) via immediate family.
Closed head injuries tend to be real, real expensive, and often render the injured party incapable of paying expenses.
Your hand protection is mostly your own financial risk, your decision. Your head, though, is my (as a member of your risk group via insurance or unpaid hospital bills) financial risk, so I may feel I have a stake in the decision. I haven't decided where I come down on the whole issue, but while I usually tend to very strongly favor the individual right, in this kind of thing I also see another side as being not automatically wrong.