Baumol effects. Our economy is incredible, extremely high productivity along with full employment. Its why we have ordering kiosks at fast food restaurants, pay 225k for bucee's managers and 20 dollars/hour to flip burgers at fast food restaurants. ATC is a low productivity growth job, technology hasn't increased the number of planes or amount of airspace one ATC can manage. As other jobs and sectors of the economy improve in productivity, people migrate to those sectors from low productivity sectors like ATC because on average high productivity sectors can pay more. The salaries of ATCs rise because there is more competition for the limited pool so you end up paying more but getting the same or worse outcomes over time.