I've been skiing for twenty years and have never worn a helmet, and I don't plan to start.
I can't really put my finger on why, I just don't want to!
(I don't cycle much, and I don't wear a helmet for that, either)
On imposing speed restrictions - how could that be enforced?
What is "too fast"? If you set an actual speed limit, you have to have some way for people to know how fast they are going, like the speedometer in your car. Not really practicable for individuals.
It's a knee-jerk reaction to one incident - how many thousands (millions?) of people ski each year without coming to any harm?