Why do teammates that play even with a DC still get the full LP loss?

No, I'm not talking about the beginning of the game. The "remake" system is supposedly gonna stop this. I'm talking about when you're 20 mins in, and let's say you have a 0/4 Gangplank Top and he decides to ragequit and never comes back. Your team loses. Why do the other 4 players get punished with a full LP loss? That's some BS right there...