How does motorcycle insurance compare to car insurance?

The amount of property damage / bodily injury that can be caused to others by the negligent operator (where liability coverage will kick in) is much lighter in case of motorcycles than a car, hence liability insurance for motorcycle is much cheaper.

The risk of physical damage in the even of collision is much higher for motorcycles (Small crash can easily cause a total loss.) Also comprehensive losses (example: theft) is much greater for motorcycles, hence cost of comp and collision in motorcycles is much higher, assuming other things (values, drivers, locations etc.) are the same.