@mike_mapple
I think both golf and tennis are great examples, as is skeet or trap or sporting clays. In all three of these I can very clearly demonstrate why it is easier to get into any of them than it is to get into waterskiing. But also how they are quite similar and quite different.
Equipment costs - in all of these sports they are similar in that you can get started with a base level equipment/gear maybe even used gear that will do what you need all of these sports. Then they all ramp up quite similarly. No one owns one racket or one set of clubs, no one owns one shotgun. They all have "uniforms" be it vests, sneakers, ear protectors almost all require a hat and glasses to get through a day. Costs for a good slalom ski and bindings to get started used 500 bucks? Cost for a used shotgun similar. Top end costs buying a new shotgun or a new slalom ski? Well it can go pretty high but these are all personal costs.
Venue. Tennis benefits from public clubs, as does golf, shooting is more similar to waterskiing many of the shooting clubs are fully private. But golf and tennis has that as well. What does it cost to join a Golf Club in a busy suburban area - a swanky private club? I know of a few that have buy ins that cost more than houses. Some of them have tennis courts. But all of these things have something in common. In most areas I can find you a public tennis court with nets, a public golf course with tees and holes, a public shooting range with throwers. Pay for rounds.
What is hard in slalom? Public or open to the public waterskiing.
There are clearly exceptions but I can go to darned near any city that has lakes and find a place to shoot trap, play tennis, or golf just by googling it. If you want to pick a city and pay good money to get a ski set... well that's also expensive but also probably cannot have it happen.
And a golf course is surely more land than a ski lake and has tons more water.