Why do luxury home makers or the rich build tennis courts into their house plans?

I understand maybe a pro tennis player doing this but is it that much of a coincidence that about a quarter of mansions have a tennis court? Is that prime piece of property really worth wasting over a tennis court? Are they THAT much of a tennis enthusiast that they just HAVE to have a court to play on taking up half of their backyards?

Well if you play tennis and find you like it you always want to play and having the convenience of your own court is nice. Also tennis considered a gentleman's sport. A sport for ladies and gentlemen.... hence rich people and mansions have tennis courts.... since many people believe tennis is a sport of the high class because of it being a gentleman's sport and the Etiquette.

Very many people play tennis as a form of exercise