The ghost has it partly correct... airports are for aircraft activity only.. the Feds do not want to see airport operators spinning off point to find ways to make more money! This is not a new issue nor is it aimed at R/C aircraft or Jets.

Here in Colorado a several years back we had an airport operator that discovered he had a car race track ready made.. or at least the race car enthusiasts discovered it... anyway you can see that if an airport owner operator is having hard times making it with airplanes why not open it up to anything that pays. Can you all see what could happen to many little airports across our fine Country..

I believe the non-aircraft usage hat trick is pulled out when either the locals or the Feds don't want "it" to happen! The Feds on the other hand will pull the non-aircraft usage trick out of the hat when they can see the local airport operator is getting out of hand..
Lee H. DeMary
AMA 36099

Edited because of the Quote killer thing