Those 30 to 40 somethings are busy with their kids and busy paying to raise their kids.
I have always loved aviation but didn't have the money (and more importantly the time) to take it seriously until I was in my 40s. Bought a plane at 42 and learned how to fly.
Now, at 52, I'm thinking of selling. I'm changing careers and probably won't need a travelling machine any longer. It's easy to justify the $4000 annual fixed costs when flying 200+ hours per year, not so much if I only fly 50 to 75.
Oh, I could easily afford to keep it but have better uses for my money and thus it may be time to go on to the next adventure in life while at the same time going on to my next career.
I may buy a "toy" plane, or just rent when I feel like flying. But probably not because my attitude these days towards flying is...mehhh...BTDT GTTS.
First, though, I need to determine what my next career will be (if anything) and make sure it won't require a travelling machine. But, if not, I'm out. At least that's the way I'm headed.