Why do people who own private boats/small yachts never use them?

In any upper-middle class or higher, urban/suburban area, near a large body of water, there will be docks packed white boats, yachts, and sailing ships. These are privately owned and are always pure white. All the time the docks are PACKED with boats. But there are never any boats in the water, nothing further out at sea, and zero human activity on the docks. It's like this year round, all day, and regardless of the weather (so no it's not temporary factors). I've seen this in several cities, multiple different US states and countries.

I ask because I'm kind of interested in getting into sailing and getting involved with "boat people", it seems like fun. But the fact that I never see anyone doing the activity is a bit offputting