Another factor that may enter into the equation is the ongoing urbanization of America. I live in a rural state where our total population has changed little in the past 100 years, but whose cities have grown exponentially and whose small towns, outside of oil country, have steadily declined. Farms are getting bigger and both farm kids and retiring farmers are moving to the cities. I doubt we are unique.
With more people living close to a commercial service airport, fewer people see a benefit in flying themselves for travel. And almost nobody gets started in GA without at least some dream of traveling. Even the people who just make laps in the pattern and occasionally go for a $100 hamburger probably didn’t start their training with that as the sole end goal.
I’m an exception that proves the rule. I keep moving more rural and using my own plane for travel more, with a dream of upgrading to something pressurized. Even without filling the seats, I can compete with airlines on time and (marginal) cost. Having to leave the day before a trip in case roads are bad and stay in a hotel to catch a 5 a.m. flight that’s necessitated by connecting flights, having to leave my dogs at the boarding kennel, and other things all add up in dollars, hours, and anti-enjoyment. If I could take a $10 and reliably 30-minute Uber to the airline terminal, I’m sure the plane would fly a lot less.