If they stopped providing services to FL180+ non-part-121 traffic they'd see way more reduction in load than just cancelling a little 121 traffic. Idk if anyone has looked at the unfiltered flight trackers but there are a fuck ton of private/business jets up in the flight levels and they're not flying as predictable of routes (usually into smaller satellite airports near the main ones). They can't do that though because it would upset all the rich people.