Not to be a smartass, but in all honesty, there are a couple things at work IMO. First is how many of us ever hit the top of our respective professions? I mean the TOP?
Now consider how many of the one or two possibly that have could sustain that level for decades? One? the other? Neither?
THEN add in the nebulousness of being creative pitted against the changing tastes of the audience. If you take 1000 fans of a band at 16, 800 will be into totally different music at 30...while the new kids may not like your thing at all.
IMO, it’s a miracle a band like AC/DC (who I love)can get any real longevity at all. Any band really in ‘popular music’ since that definition varies lately by the literal week thanks to Beatport and the like.
TLDR version...IT’s HARRRRRDDD!!!
What you state is so true for the music industry for some strange reason and for reasons you state. However it is not true in the business world where I belong. I have been at this for decades and working harder and smarter than I ever did. Same with most older people I work with. I’m at my peak and getting close to retirement.