In the new Star Trek movie, why doesn't old Spock just leave Delta Vega?

I don't get it. So, old Spock (or "future Spock") is marooned on Delta Vega after he has gone back in time by accident and caused horrible things to happen. He is living on this frozen planet with huge monsters. He is 14 kilometers from a Starfleet station, with a small staff, and he knows how to travel back in time. So why hasn't he already gone back in time and fixed everything? Why does he just wait there until Kirk happens to come? And if he's content to just sit there all that time and wait, why does Kirk's arrival change his mind? I don't get it. Is there some reason he stays on Delta Vegas all that time, and doesn't realize he should just travel backwards and re-do things so that all the horrible things don't happen??