Wheels are pretty solidly mounted to cars with large pieces of metal. Tires do blow out however then you still have some control. Props on the other hands can

Wheels are pretty solidly mounted to cars with large pieces of metal. Tires do blow out however then you still have some control. Props on the other hands can have electrical component failures, wiring failures, engine failure, bird ingestion induced failures, control instrument failures, etc. Remember that each vehicle has four times these components (ie: four times the failure rate) and the failure of any is a crash. Just a lot more potential things that can fail and cause a catastrophic accident.