I believe everyone here has hit on a solid reason for their locale, but sadly there is no "single fix" bullet for everyone. I think RumLine hit the nail on the head above though, dig deep in your demographics...
I also believe TIME is a HUGE factor. Growing up in the 70's, the "dads" all worked 40-50 hr week and had short commutes; moms were home with the kids. Now it seems everyone I know is working more (~55-60 hr/wk) - and that's BOTH both parents -- and have a considerable commute on top of that; kids are dropped off at before/after care places until they are picked up by mom or dad. They also enroll their kids in these "advanced TRAVEL sports teams" that eat up severa evening a week and the entire weekend -- most are tournament style games, two on Sat, several hours apart as to rest, and as long as you're winning you are coming back the next day. The games are anywhere from 30-200 miles away, so it ain't like you are gonna be running back and forth; several games require hotel stays. During these weekends, the kids fill down time with portable electronics and DVD players in the SUV. The parents fill the gap by staying connected to their cell phone, either answering email, work email, and catching up on their sports teams. This is the norm for many parents my age in my area. I just don't understand putting your 9-12 yr old in advanced "travel" games at this age. I can only surmise they are hoping for a college scholarship way down the road???
I saw the light a few years ago, moved jobs to greatly shorten commute time, cut back expenses so wife could scale back from full time employment to be a teacher's asst at the neighborhood school, so she's home when the kids are home, especially all summer. You know what, in the end w didn't have to scale back much at all due to all the money we were saving in before/after care for the kids, gas, etc.
Almost impossible to get my friends sailing due to their schedules explained above. Even Wed night races are out because they either work too late or are playing ferry to take kids sports practices.
In addition to time, I also believe it is also somewhat tied to a "lazy" mentality as well -- the parents I know are 35-55 yrs old. They can drive their kids around to games/practices, hang in the background surfing their phones, sit and watch their kids play, all the while "relaxing" themselves. Same goes for when they park their butt on the couch to watch a pro game every chance they get.
Although sailing IS time consuming, I don't see it as any different than drowning your kid in sports. However, you may have a hard time convincing others of that mainly because it would require them to get up off their butt more often to wash the boat, perform some maintenance, and prep for the boat for an outing.
Unless people wake up and make a lifestyle change to free up time and WANT to get off their butt, there is very little any of us, or even a yacht club can do to promote our sport -- but a demographics study might prepare the yacht club if/when people do make the time to see what it's all about.
Side note, I know several families that have trailer motor boats and most are often too lazy to take those out as well. Could be due to overdue maintenance or cost of fuel, but I believe it goes back to they "think" they have to work all they can and then want to lounge whenever they can -- a boat is just too much work!