It wouldve either caused a paradox, where he would no longer exist on our time line Or Nothing wouldve happened, because there is only on timeline, so any attempts he makes wouldve been useless wastes of energy. Or (how i view timelines) Because there is no way to create a new timeline or transfer yourself to another timeline, he [i]already has[/i] been to the past, which, obviously, did not work (see point two). So now he uses his timetraveling capabilities to go into the future and warn us about games (but still, people believe that time travel is a proposturous idea, so they dont believe him)