Why stick out a clear losing battle?
It never fails. The team is down 10-30. One or more of the enemy team is sickeningly fed. Time to surrender, right?
Wrong. It always seems like there are 2 holdouts at 20.
In my mind, it is clear that this team, or members of this team, need more experience in the laning phase. Whether it was at champion select or even before, with masteries and runes, or during laning, someone on the team just didn't get it, and gave a strong lead to the enemy team.
So why fight it? Why not surrender and start a new game, and try again to lane well, learning from your mistakes? If it's obvious the game is going to end in a loss, why bother sticking it out and getting mopped up? There is nothing left to be learned. If you want more team fight experience, play an ARAM :P