The skiers were on the side of a run heading into the trees and not paying full attention. One other consideration is that even if a helmet is worn it is not a substitute for exercising good judgment while skiing. One study showed that helmets lose their effectiveness if a skier strikes a solid object at more than 12 miles per hour. The most serious head injuries occur when traveling probably over 25 miles per hour. Information is still being collected on the helpfulness of helmets used in skiing and snowboarding.
Injuries can occur and helmets can provide some protection.
However, wearing a helmet should not raise a false confidence and be an excuse to be less cautious or respnsible.