If being ATC gave the player a certain amp into of WP only after they have sent some commands in the chat or on their desired frequency, this way I think more players will start bring ATC's in already the amount of airports we have.
Bonus suggestion:
If you're an ATC and change the frequency, it appears on top of the airport name on the map, this way if we have several atc's they can freely commands without being confused because of other people's.