Quoted from Trekkie1978:

I think everyone is overlooking one huge reason: marriage.
My brother owned a boat for 3 years. Went fishing on it almost every nice weekend in the summer. We would also take it out to the Mudhole to fish for tuna and shark.
He met his wife, and the first year of his marriage, the boat got 25 hours put on it. Year 2 of marriage, 15 hours. That's when he realized it was time to sell it.
I'm sure it happens to a lot of people here. Get married, take more vacations, kids come along…and those pin dollars have been converted to other things.