Okay, here's another theory that I just made up: kids. Young adults seem to be totally devoted to their kids these days, spending much of evening and weekend hauling them to this that and the other practice or sporting activity. And there are a lot of different activities people are into these days, and many of them have high time demands, are highly competitive, and are often fairly expensive when you add up the gear costs and activity fees.

I'm also into martial arts, and the real money in martial arts is ... kids. Most (not all, but most) adults get into it only after hauling their kids to practice and watching for a matter of months. I don't know if a similar path exists for drawing in adults via youth sailing programs since I don't have any experience with them.