We're talking about two vehicles colliding with each other. The mass of the vehicle is absolutely relevant.
Crashing a bike at 30mph/50kph is not as dangerous as you suggest, you can find plenty of higher speed bike crashes on youtube with no fatalities. Road rash and broken bones are the most likely outcome. I've crashed at this speed and I walked away with road rash only.
There is an enormous difference between a bike crash which results in sliding along the pavement and a car crash.
Crashing a bike at 30mph/50kph is not as dangerous as you suggest, you can find plenty of higher speed bike crashes on youtube with no fatalities. Road rash and broken bones are the most likely outcome. I've crashed at this speed and I walked away with road rash only.
There is an enormous difference between a bike crash which results in sliding along the pavement and a car crash.