In 2009, a German state governor caused a terrible skiing accident, which he survived but the victim didn't. He was wearing a helmet, she wasn't, and after that point, helmet sales in Germany and Austria shot through the roof and use has remained high. Before that, it was pretty much only racers and children.
Natasha Richardson (reasonably well-known actress) also died the same year from a skiing-related brain bleed. And yeah, while I haven't had a lot of visibility into ski area helmet usage over the past decade, that does seem to be around the time when it really shot up.
