Why should I have to lose LP just because some idiot doesn't want to play half way into my game?

This has happened to me so many times, i'm just playing a game and i just see that one of the other players got killed, then they just rage and quit the game. I then have to suffer through a slow and painful game of just trying to just stall until the afk player decides to come back (which they usually don't) which end up losing 99% of the time. Now, I don't see why I have to lose LP just because one of the other players can't handle their rage.