When I'm taking the lane, drivers seem to focus and pay a lot more attention to me than they do any other vehicle on the road. I think that makes them less likely to rear-end a cyclist under reasonable visibility than just another car whose speed they have misjudged while daydreaming.
Motorcyclists who regularly occupy the travel lane face the same vulnerability, and serious rear-endings at signals do happen sometimes, but not nearly as often as turning or crossing collisions.