Why do I lose ELO when my teammates AFK/ troll?

So my MMR is shot and I'm a silver playing with mostly bronzies when i solo q. I never feed or play poorly, it's usually my teammates who do bad. So I lose and I never rank up cause of this. I'm a support main. TOday I had this game where this bronzie rage quits within 5 min and we play an hour long game where the 4 of us actually get more team kills but we lose cause of course we are down a man. How is it fair I lose 22 LP (when I'm only gettign 15 LP for each win) when I keep getting stuck with trolls, people who AFK, etc..?? Why hasn't Riot instituted fair ranking system whereby LP is taken and rewarded based on individual negative and positive contributions, respectively? Like if someone afk's and the team loses then that person would lose a significant portion of LP as opposed to people who didn't AFK? or if a person trolls and the team reports them , then they lose more LP as opposed to the non-trollers? wouldnt this make more sense????? I'm stuck in silver, can't escape. it's not fair i'm stuck with piss poor players..