Loss of lp from Afk/RQ players

Why is it if you play a game and a player DC's or rage quits that you still lose full LP for it? The only reason im complaining is cause i cant tell you how many times ive dropped from G1 to G4 from having about 60% of games having a player leave... and im not exaggerating. So most my games are consistently 4v5. I get life happens and you get a power outage.. or w/e but i feel if the game registers someone as afk and you lose.. you should only lose half of LP... or whatever % of game the player was absent is a reduction to loss of LP. So if a player leaves or dcs at 4-5 min in game and you make it to 20 min then you should get a 75% reduction and the offending player should be banned or restricted after so many times... Like draft games not a big deal.. but gold is already bad enough with people trolling or win trading...then to add afk or RQ to it... just sucks...