Pay is a huge part of it, so it really is that simple.
Qualified people are choosing not to even apply anymore because the pay is no longer competitive with other high-paying jobs that don't destroy you mentally and physically, or have a complicated hiring process like ATC does.
Whereas a field like tech almost requires stimulant use now. Maybe good peak pay, but no job security there anymore though.
Maybe if they apply for ATC they just don't disclose that, but I imagine if they do, it will be scrutinized.
Developers can always fix their mistakes. Very, very few would even even possibly result in the loss of life. I'd think pay for controllers should be much higher, but like anything it is subject to economics. If people are willing to do it for $X, then that is what it will pay.
Funding sadly is probably better handled as a tax on the people rather than the industry simply because ATCs protect more than just commercial crew and passengers, and more than just their home country.
So those pilots. Even their new pilots (First Officers) make more per hour than ATC.
(ATC here, opinions are my own and not that of the FAA.)