This is an interesting thread on the eternal question...
I came to golf at 47, athletic background, etc. Can't play soccer or basketball anymore (teams). I love golf and have the means and time to pursue it.
The sport has inherent challenges -- in comparison to -- other options for youth, me, everyone.
1. I can play a fairly fulfilling basketball "game" by myself, in my driveway, with a ball and the basket that doesn't change shape, cost, etc every year. If i've got a half an hour, go out back and work up a sweat, solo if necessary.
2. Anytime i want to play or practice golf, short of putting on my carpet, its an hour minimum to get to, use, and from the facility. Which in many locations is of questionable quality
3. If i want to play, its the hours noted above. That's not going to change even if you play 9 or 12, its 2-4 hours. Thats a huge amount of time for anyone, in any situation. If you do 2-4 hours or more of something in a day, its going to be work or sleep, maybe golf!
If we get 50% of income from 20% of the players, it reflects 4 of 5 who even "agree" to embark on the golf journey do not or cannot embrace it fully. I suggest thats due to the inherent nature of the sport - you can't change what you are, or who you are. If I like to sail, i gotta have at least a raft and water...
If we got to 2005 with these assumptions and realities, I bet we'll make it to 2050 with the same sport that some pursue passionately and many more have a passing acquaintance...