I don't believe that a lack of money is keeping people from sailing. As you note, if you want to sail, you should be able to do it cheaply.
I started sailing in 2003 with a 1982 Catalina 22. I paid around $3000 for the boat and it was in good condition (not great, but certainly good enough for day sails). The boat was on a trailer and came with a decent outboard engine. I could not get a mooring that year so we trailer sailed the boat. I paid the town $10 for a ramp permit so I could launch the boat, park the car and trailer, etc. I would have to check my records but I think I sailed the boat 5-10 times that year (got the boat in early August).
The next year I paid $100 for a mooring permit, got a free dingy that I fixed for $50, bought a mooring for $300, and paid a company $100 to drop the mooring and $100 to pull the mooring in the fall. So my total costs for a year were under $1000. We sailed a lot that year (upgraded to a Newport 28 in July, but that's another story)
But sailing is not for everyone. It takes a serious time commitment and the right personality and I think most people are just not into it. If you have a family with kids there are so many competing activities that most people are not going to make the commitment to go sailing. Between work, kids sports, house, lawn, and vehicle maintenance, family obligations, TV/computer/video games, etc. there just isn't that much leisure time available. Then the weather and seasons come into play too. I'm in the north east, and the sailing season is really May - October. And in those months, how many free weekend days will there be when the weather cooperates? How many people are willing to learn a complicated activity with a unique language, that is sort of anachronistic (you mean we can't go directly from here to there if the wind isn't blowing right?) and perhaps dangerous?
Then, when you finally are able to get out on the water, and the weather is nice, and the wind is nice, and the boat works well, MOST people are still going to be like: "So this is it? We're on a boat and going like 5 miles and hour, and we can't get anywhere and why can't you turn the motor on so we can go faster, and like I'm hungry and why didn't you bring anything good to eat and like I'm so bored, and my iphone is like dying, and OMG this is so boring, and I have to meet my friends in 2 hours and when are we turning around and why is this taking sooo long."
Wow, writing all this down, I wonder why ANYONE with a young family sails. I guess that's why so few do!
Personally, I LOVE sailing and I AM a little crazy, so it works for me. But certainly not for everyone.
PS: For SOME people (those who GET it) when you finally are able to get out on the water, and the weather is nice, and the wind is nice, and the boat works well, it will be like "This is amazing! It's so peaceful and quiet, and the boat moves through the water so nicely, and this is all free? And we can go anywhere we want and food on the water tastes so much better and the sun feels good on my skin and we can stay out here as long as we like and how does the boat move so well when I can barely feel the wind and the water is warm and THIS IS JUST GREAT!"
Just wanted to comment, we just took up sailing. Kids in and older than college. The moments when you have a good breeze, and the sun is glinting off the water, and the wind and sun are on your face, with no noisy motor, slicing throught the water as people have done for thousands of years- well, this is what makes life magic. Those "in a rush" people? Maybe they'll appreciate it next time around.