Statistics show you're far more likely to injure a leg than any other part of the body, and that most injuries are caused by falling or landing badly after a jump, than by hitting someone else (in which case a head injury seems more possible in a one on one collision).
https://www.premax.co/au/blog/recent-statistics-on-skiing-and-snowboarding-injuries
Add in the additional safety feeling that wearing a helmet provides (in all sports) increasing the likelihood of taking greater risks, and helmet wearing doesn't really seem a big issue.
But don't let me stop you.