The actual reason for a pilot shortage is due to fewer military pilots which used to transition to civilian pilots. It has nothing to do with the Department of Transportation.
Or the fact that the lifestyle is shit in most airlines. There is a shortage on other continents too, as in Europe where you can fly Boeings with less than 300 hours.
There are plenty of candidates, but they must pay for expensive training and type ratings (specific aircraft model training) that most airlines are unwilling to pay for, they used to.
Most airlines hate pilots because they cost money that should go to shareholders, so they would rather overwork a few than hire more. Conditions worsen year after year.
The constant sleep schedule runaway shaves a good chunk of your life expectancy. You have little control on where you live, no family life. Wanna go to a wedding? Just request that day six months in advance in a web portal and see it tell you it’s denied. That thing your kid wants to see you at? We don’t care about that! You’re married to your job.
Younger generations don’t want that kind of life, and also are more environmentally conscious, which doesn’t help.
*I have no first hand experience in flying for a US airline but I know it’s similar. Edit for typo.
The other reason, also related to military, is that a couple of months ago the FAA integrated their records system with the VA. Because of some records disparities, specifically health records, thousands of pilots have had their license suspended. This happened to someone I know and they got all their documentation to the FAA in early April and as of 2 weeks ago they were told to expect 3-5 more months of a wait before it’s reviewed because they’re so bogged down
The path for non-military folks to start from private pilot and end up at airline transport pilot is technically there, but unless you’ve got a bunch of money sitting around, it’s very prohibitive. And with pilot salaries being what they are, and not what they used to be, it’s an even harder sell.
The 1500 hour rule means before you can fly folks in these commercial settings you have to have a LOT of hours. The way a lot of non-military folks do this is by being a flight instructor for many years - living on pennies. Then they can finally go work for a regional airline and make pennies.