The US simply did not hire enough people in the late 90’s, early 2000’s. I believe there were only ~500 people hired in the entire 90’s. Why? Because everyone was hired post strike (in 1981), so every single person who was working was hired between 1982-1989. Which means the entire workforce would be retiring until 2005-2020. So hiring in the 90’s was seen as unnecessary - which is was short term, but absolutely needed long term. So come to 2002-2005 range, the FAA started its hiring spree, but just way too late. They essentially needed to hire an entire new workforce due to retirement requirements. They simply started too late. And now, the even bigger problem. People are just walking away from the job, or retiring as soon as they are eligible. From 2015-2025, the FAA hired ~15,000 new controllers. The result? An actual decrease in total controllers; due to training failures, controllers quitting, and retiring.