However, I can't say that I will never be in a wreck that's my fault, or at least that I'm responsible for (my fault: I'm not paying attention. My responsibility: my brakes give out). However, I think that motorcyclists can cause unnaturally high insurance rates because wrecks with them are inordinately costly. Motorcycles cause everyone to get much more insurance than they would if it were just cars.
Sure, just motorcycles could work, except that some of us have children, and in some places, it rains or drops below freezing.
Rates are influenced more by the cost of repairs (inflation) than by the cost of injury.