There are a lot of times where players leave during a match because they where going to leave anyway, especially when its quick aikido or 1 on 1 or few people are playing, a lot of the time people leave when in a match when it has barely started too, and if it only counted as a loss after a certain amount of frames had passed, you would have to figure out how many frames it would have to be. And people could easily scam/farm or whatever for qi because if it gave you a win and the person who quit a loss you could just have someone constantly rejoining and leaving the server once the match starts.