>why quit a game without notice thats cheating
No, it is not. There is no rule on FOD saying you have to
tell
an opponent when you are going to leave after a game. What you are doing is creating your own rules that you think people should abide by. No matter how much you argue it is not cheating because it's FlyOrDie who creates the rules.
It happens on all FOD games, people leave after 1 game of pool/snooker (When some people expect best-of-3 all the time), same goes for many of the other games. People often don't want to play more than 1 game or don't have the time, it's just something that will always happen on here. It may be unsportsmanlike/impolite but it is not cheating ;)