Why do people do this?

I just played a game with a Zed who said he had to go 10 minutes in so he wanted us to open up mid so they could push and finish but we said no. Since we weren't going to open mid and we didn't surrender at 20 he just started feeding. He ended 0/12/7. If you think you have to leave don't start a game. If you really want to play but don't know how much time you have play bots. At least in bots you know your team can still win a 4v5 against bots. Do not start a public 5v5. If something important comes up during the match that is different but his situation clearly mustn't have been that important since he was there until the game ended at 33 minutes.