Pilot error is THE reason. Radio "shots" is THE excuse. I think Marconi really did get shot down once. Pretty rare after that. I watched a guy tip stall and snap right into the runway 2 weeks ago. He swore someone turned on a trans at the swap meet. Everybody ran around taping all the transmitter switches. It worked for about an hour until another guy tried to fly an obviously tail heavy plane and was also "shot down!"
Tom