Perhaps it isn't JUST the disposable income - but also the fact that companies nowadays seem to expect you to work 24/7 in addition to the lack of rise of income. I rarely work less than 60 hours per week, neither does anyone in my immediate circle. A good friend of mine is currently learning at North Wealds, and he cannot dedicate more than half a day a week to his learning as a result of the pressure forcing him to work very long hours.
I think that the ever increasing cost of flying far beyond normal inflation is also something to do with it. Avgas often at £1.70+ a litre (in the UK) often €2.50+ a litre in Europe (and thanks to Brexit et Al. that's currently £2.27 a litre excluding transaction fees). Touring suddenly becomes less affordable, and to spend £10k+ to learn to fly, just to go within 50nm of your home airfield quickly gets boring (which I have found is an important factor for the decline of pilots staying current).
StepTurn - am I wrong in thinking that it is quite difficult to find somewhere to learn on older types / taildraggers? I have always wanted to fly vintage aeroplanes such as Tiger Moths, PT-19s, Norseman, Waco....etc... But every single time I inquired, the market was very much more leaning towards "scenic flights" with an instructor. It seems very difficult to get access to a vintage plane, and be able to fly it solo after learning the differences, and proving your competences. I am sure that this is for good reason, but this to me is prohibitive to spending thousands upon thousands of pounds to get the differences required to then be told, well now you can fly it with an instructor. The only place that I have come across the ability to do this was in Wanaka, NZ - where I decided to do a substantial amount of mountain training instead of learning to fly a new type.
Scary thought - would you need a pilot if there were no controls and everything was completely automated? What happens when the sensors ice over in freezing rain? What happens when the plane has some emergency? Or worse - electrical failure?