>>1429281>>1429302>>1429323They're designed for similar impact speeds as a bike, keep you warm and provide extra sweat in the summer, keep you from getting bicycle-induced leather skin (cancer), protect you from face-mutilating hazards, and you don't look like a fucking idiot while wearing it.
Racers would suit up like pic related with NO helmet if the gay UCI allowed it. A normal bike helmet is only effective if you land on it.