What's stopping the same materials and gear being used to create cold-weather cycling kit? Nothing, it's just that there's a lack of a need for it, because the roads would be unsafe at the temperatures it would be needed at.They are also equipped for it. Anyone goes skiing you have a ski jacket, pants, boots and thick socks. Ski jumpers and alpine skiers have tights and clothing designed for speed but are designed for maximum warmth in freezing temperatures. It wasn’t all that long ago that a cycling kit required you to stick newspaper down your jersey so your sweat didn’t freeze on the descent in stifling heat.
That is my point. Hansen's letter cited the cold as the danger, but the cold is not what causes the problem, because, if equipped for it, they could easily race in the sub-zero temperatures. Hell, cyclocrossers already do on occasion. It's the road conditions at those temperatures that make racing in them unsafe for road cycling, not the temperatures themselves.