Hiring controllers is not easy. A friend's daughter just went through the hiring process. She graduated from college with an appropriate degree right as COVID hit. Her FAA application wasn't accepted for four years.

This past summer she did the four-week interactive online courses. Applicants must pass this and may not re-enter the program if they do not. After that she did the six-week courses in Oklahoma City. Again, applicants must pass this and may not re-enter the program if they do not. She passed. Only half her class of 20 passed. In the prior class, only 4 of 15 passed.

She declined the position when they could not offer a position within reasonable proximity of her family. She, too, may not re-enter the program. On top of all that, the program has strict age requirements because there's a mandatory retirement age (55, I believe).

There isn't a large pool of applicants and the percentage of successful ones is not high. Considering the amount of lives on the line, it's understandable the hiring criteria is strict. All told, it's not an easy position to fill and even explicit efforts to increase the number of applicants will take years. Just like many other skilled fields.