Why do i constantly lose 19-20 lp for afk on my team?

Riot, that's not even remotely fair. Why do I lose 20 lp when my team was crippled because our support was AFk from the beginning of the game.........

Not fair, and it's bullshit. Why is nothing in place for compensation?? How can your system not tell that someone dc'd and was afk since the start of the game? How can I lose 20 lp when I was playing the best on my team?

Honestly, i'd like a decent answer from someone because there needs to be an explanation.