If they want to give up, its probably best to. Quitters will always want to quit. The only way they will want to "try" is if you are somehow dominating and you will carry them, requiring them to do no work really. It sucks, but its just how people are. I kind of wish you could report or award people for being quitters, but I feel that would be "toxic" and "negative". Anyways, being behind has a lot of advantages, at least in regards to team play. As you are behind, you HAVE to play together as a team as it is really the only chance you have left to pulling off a win. Grouping earlier and pushing for objectives (towers, dragon, baron, buffs) will help you be able to secure them just through numbers and damage, as you should be able to win a 3v5 or 4v5 if you aren't TOO far behind and have CC. You are forced to work together as a team and this is your opportunity to make it back into the game. If you fail after trying or the other team rallies together, though, you might lose if they do it soon enough and then you are probably better off surrendering.