That would be my default thinking as well. And "follow the money" would reinforce that thinking.
But I would like to relate an anecdote that may or may not have a bearing:
About 10 years ago, on the last day of the ski season, the local hill declared that they would run the lifts for free that day. I hadn't skied in close to 10 years, but I figured, it's free, I hadn't been in a while, and it was close by. Put my, at that point, approximately 25 year old gear in the car. When changing into my boots in the lodge, when I put the second boot on and tried to close one of the clasps, the boot literally exploded around my foot.
I was glad it happened then, and not on the slope. Best I can figure is something in the plastic gradually off-gassed over 25 years, leaving what remained brittle.
Just one anecdote, maybe means nothing. Don't have any idea of how related the plastics making up my boot are related to the stuff making up modern helmets, and hopefully advancements in materials science over the last 30 years has resulted in far better performance for modern helmets. But, as Rod Serling might say, "Submitted for your consideration".
TomK