It's not hard to work out, is it? People want to earn £40k+ rather than earn next to nothing as an FI, bush pilot etc.
Are people getting into flying at such a young age for the right reasons if all they want is the big money?. Plenty of other jobs around that pay the same or more without the effort required to be a pilot.
Speak to most airline pilot who've been doing the job for a few years and they are bored out of their minds flying SOP's day in day out. For a 20y/o, 45 years is a very long time to be stuck doing a job that no longer interests you. Even just a couple of seasons of bush type flying isn't going to make much of a dent on their overall lifetime income, but the experience gained will certainly last a lifetime.