If a moto can't avoid running over a fallen rider, it was following too closely. Why does a race moto need to follow close behind the riders? Photographers should use longer lenses, commisaires can follow the action from 100 feet, etc.
Bike racing needs to establish and enforce rules for how close the motos may get to riders, how fast they can pass the riders, reduce the number of photo motos, and punish motos involved in accidents by excluding the moto rider and the passenger for a significant period (1 year).