Flying used to be a glamorous activity
Yeah, very true.
However, this is not a recent thing. Romance went out of private aviation decades ago; probably before WW2.
A slightly more recent thing is a general uplift in peoples' expectations. In the 1970s, standards everywhere were pretty disgusting. I remember going to exhibitions and air shows, where the toilets were disgusting and the food was crap. That's all gone today. But "we" still fly the same 1960s crappy planes. A lot of people today won't climb into a knackered old 1970s Cessna/Piper. I had a trial lesson 10 years before I started flying and I remember the radio was held by 1 screw and about to fall out. That put me off for a long time.
There has been a big decline in PPL issues in the last decade - about a 1/3 drop. That is probably something else. I don't know if anybody has done an analysis of whether there has been a change of the student pilot age profile, but younger people have so much else nowadays bidding for their time and money, and I would expect their numbers to be declining.
Anybody that tries to sit down and rationally run the numbers is probably going to have their aircraft up for sale within a matter of hours
Well, yes, but you could say that for horses (which as I well know cost an obscene amount of money, as well as creating more emotional issues (for women) than anything else including kids), boats (which cost loads of money and have absolutely zero utility value), and just about every sort of sporting activity. At least GA has utility value - once you drag yourself above a certain level of capability.
Unfortunately, a "certain level of capability" equates to
ownership and nobody in the training system is going to promote that option...