rage quits

Why are we, as a collective, punished because someone on our team rage quits? This is especially painful in ranked. I just had a game where my top fed 4 kills to a darius because he was a plat riven main not a morde player but we are playing in a silver game. But instead of farming safely under tower, which he could have done easily as morde, he dies over and over then rage quits. Enemy team literally wins before we could even hit surrender and I lose 20 lp again.

Why?

Why can we not have some fail safe system where if someone leaves a game and doesnt return for 4 to 5 mins we can initiate an early forfeit where we dont lose LP, enemy team still gets their free win but the rage quitter lose lp and honor?

I know some will say its abusable, but it will be mostly abused by those who rage quit anyways as most people want an actual game.