My guess is the airlines are funding most of it because they're using most of it.
Not much need for triple parallel PRM approaches (and the requisite runways, facilities, radar, controllers, etc, etc) in East Ruralsburg, Wisconsin.
"Buh, buh, buh, the corporate guys use some...."
Yup, they do. I don't see many phalanxes of Learjets descending on any one destination at one time, requiring tens of square miles of ramp space, either.
Aviation is a game of exponentials. If you want to squeeze a LOT of airplanes into ONE spot of concrete in a very SHORT amount of time, it's going to cost WAY more than the multiple of flagging down 5 Challengers an hour.
In the end, the game is about concrete. If you have enough runway per delta T, you don't need NexGen, fancy PRM approaches, RNAV arrivals or hordes of controllers. It's when you don't that it gets insanely complicated and wickedly expensive because you can only have one airplane occupy the strip at one time, and the amount of time has a minimum floor to it. You need to extract every trick in the book and then some to ensure that you can pile enough airplanes into the sky stacked and ready to utilize that finite time.
Outside the heavy usage periods, most of that fancy tech and spare concrete goes to waste.
So sure, some people get to use the fancy tech that someone else probably paid for, but it's irrelevant because they don't need it, and could get along fine without it.
I love the GPS in my airplane. Use it every trip. Glad the military picked up the nickel on that one. But I got along fine with the VOR, and could still make 100% without GPS. And a VHF shack in someone's field is still WAY less expensive than blasting a nuclear clock into orbit on a tube full of explosive juice.
Richman