I've said it before in these types of threads and I'll say it again, what is with the "fear" of the declining interest in sailing??? I just don't get it.
If you like sailing, and have a boat, and are out there doing it, as I am, then I just don't see why anyone cares what anyone else cares about.
In fact, if the waters in which I sail become less crowded over time, great!
I don't need other people to enjoy sailing for me to enjoy sailing.
For many people sailing is a mix of both a solo and a social activity. The lake I grew up on had an active "Yacht" club which held weekly races of multiple dinghy classes along with an annual invitational.
In spite of a having much more affluent local population today and being one of the largest lakes in the metro region there is no longer any regular racing on the lake. The Yacht Club still exists as far as I know but has a declining and aging membership.
This means that for the people on the area there are fewer opportunities to race or even share their love of sailing with one another. Not only that but sailboat dealers are fewer and farther between. Parts (and boats) get more expensive because manufacturers deal in smaller volumes. Right now there is a glut of old boats on the market but this will change over time as fewer new boats are being made.
I don't think this is strictly tied to economics. There are lots of leisure activities that are not only cheaper but less time consuming and which can be enjoyed with little or no learning curve. Pretty much anybody can hop on a personal watercraft and be zipping across the water in a mater of minutes. Same with kayaks or paddleboards.
I belong to a local sailing club and what is astonishing to me is the high percentage of people in technical fields that are members. Just a guess, but I'd say for these people, learning and honing the somewhat arcane skill and language of sailing is part of the attraction.