AFK in ranked

Ok so top is AFK. Hasn't moved, hasn't got items. I'm sure the game sent him a warning and all that so the system knows my team is at a clear disadvantage. Why do I have to lose LP because of it? Yes I recognise that if riot decides to give the team with the afk a free pass that can be exploited. But if someone is afk from the start , why do I have to lose the full amount as if I lost playing a fair game? Surely 1/2 the loss of LP is reasonable