The biggest problem with waterskiing IMO is not just that its inherently expensive. It's that it also inherently serves a small number of people. You can invest millions of dollars into a golf course and have dozens of people playing on one 18 hole course at any given moment, or invest millions in a ski resort and have hundreds of people snow skiing at any given moment. You may have to pay a lot as a customer to go there, but at lease once you pay you're given immediate access to hours of fun.
You can invest millions of dollars to build a 2, 5, heck even a 10 lake site, but you will still always be limited to 1 skier per lake every 10 minutes (or however long a single set takes). Compared to other high cost sports, that's a ridiculously small capacity. The problem isn't just that there's not enough people who want to ski. Its that even if there were, there wouldn't be enough places for them to go.
So what's the solution? I don't know. The problem is inherent so its not like we can just have multiple people skiing at the same time on a single lake. Perhaps we need to focus more on adding entry level activities (similar to creating 15 inch golf holes) that simply exist to a) increase visibility of the sport, b) increase revenue of ski sites to allow them to continue serving "pure" 3-event skiers without going under, and c) hope that some percentage of those who come for the lesser activities eventually transition into 3-event. In this regard, sites like Trophy Lakes come to mind for me. On top of their ski lakes, they also have a cable park and a disk golf course. These things don't get in the way of 3-event skiing, but they give the site a whole lot of extra revenue to be able to keep the 3-event lakes open.