A couple years ago the transportation secretary tried to get funding to hire 2,000 more controllers. Congress said no
https://thehill.com/regulation/transportation/4617992-buttig...
https://thehill.com/regulation/transportation/4617992-buttig...
The FAA has a $5.20 tax per flight segment per passenger and a 7.5% ticket tax. The budget set by congress limits how much the FAA can spend on air traffic control, and the surplus (there is a surplus) goes into the AATF: https://en.wikipedia.org/wiki/Airport_and_Airway_Trust_Fund
This is a direct cost of American austerity.