Let's say rather that the least common denominator reason for living is that, well, death sucks. Yes, of course are positive reasons to live, and while those are nice to have, they aren't as universal a motivator, I think, as simple fear of death.
Shakespeare: "For in that sleep of death what dreams may come...?" Or as brilliantly stated by XKCD, you end up going back into the "Lego box" http://xkcd.com/659/
To define what sucks about death is the concept of complete non-existence and the the total erasure of everything you ever were and consequently destined to never exist again.
Your atoms may change into different forms but you will never experience it. That to me makes even the worst of life experiences better than death sentence known as "...we owe god one death."