One reason I wear a helmet is that I have behind-the-ear hearing aids for both ears. They cost about 2000 dollars each, so losing or damaging one in a fall would be a major expense as well as a big hassle to do without it until I could get a new one ordered and programmed.
I can hear more clearly with hearing aids under a helmet than no hearing aids and no helmet, but I do get some problems with sound feedback (caused by the close proximity of the helmet to the hearing aids). Next season I'm going to experiment with an external microphone system which should eliminate the feedback problem. I may get a new problem of wind noise, but I think I can solve that with suitable shielding.
If I'm skiing solo being able to hear well isn't so crucial (although sound is a surprisingly important sense when skiing - try skiing with ear plugs in if you've never thought about this issue). But if I'm skiing with the family I like to be able to hear, especially when the children are chattering on the lift. Quality family time implies being able to communicate with each other. But since I've got used to wearing a helmet anyway, I use it all the time.