"Hiring more controllers costs money. Who is going to want to pay them? - not the GA pilots wanting transits, and why should anyone else?"
And the answer to that is: The GA pilots do not want transits. They only want to fly in that airspace, and they would be just as happy were it uncontrolled. Since it is the heavy iron who needs the airspace to be controlled, they pay for the service. But they only pay for the service; they didn't buy the airspace.