Here's my two cents. I recently quit after windsurfing for about a year. I learned when I lived on Maui and moved to Oahu for school. I used to go on Maui 3+ times a week and I learned alot, had LOTS of fun. I got some good equipment cheap from Euros that were here for the summer and sold it when they left.
But when I moved to Oahu it was different. The spots here outside of Kailua are few and harder. Like Diamond head. Gusty, reefy long walk, bit too advanced for me. And the wind is not the same at all. I went to Kailua some in the beginning and took out my 90 liter and it was gusty and not good, and I was told(and experienced) my equipment was Maui equipment, not big enoug for Oahu. My boom only held up to like 5.8. Mast too. Had no bigger sails. So Instead of buying new(used) equipment I sold what I had and quit. The surf is so good here I was less inclined to WS and I got a sail boat, so I can still sail.
So my point is, I lived in the best WS place there is, maui, and I thought Oahu was up there too, and it probably is, so if I quit living here, I can't imagine people oding this sport in any but the best places in any significant numbers. It's hard, expensive, fickle, lessons are expensive...