I have a friend who quit playing the piano after about 13 years of practice, just 2-3 years short of her diploma. Watching her playing, got me interested in playing too, never had the patience to study though.
The reason she quit? Her teacher didn't manage to be a concert player, and tried to make one of her students. Putting so much pressure cracked some of them. In addition to that, when you urge a classical taught teenager to "play something" he/she usually will play some classical stuff. Not a sure way to have fun among teenagers.
Bottom line: She got sick of playing. The old upright piano is in the house, but I doubt if she has played more than 30 minutes in the past 10 years.
I, on the contrary play at least 45 mins every night in a humble keyboard. But nobody urged me to study for 12-14 hours a day.