Why does Riot not have loss prevented for 4v5 ranked games?

Just had the classic toxic ranked experience: our self proclaimed pro yasuo main (should've taken the hint and dodged immediately but oh well) fed and blamed literally each and every one of his deaths on either our jungler and was just generally a dooshnozzle to everyone. Eventually, our ADC admitted that he was tilted, and soon thereafter left the game. We played for probably 7 or 8 minutes in a 4v5 when we finally just decided so ff at the 20 minute mark, as they were already pushing into our base and we were down 20 to 3 in kills.

My question is this: why have we made it to season fkin 6 without some kind of Loss Prevented mechanic for this? I know that they are toying with some system that automatically ends the game if a player is afk/dced for an extended period in the first few minutes of the game, but that does absolutely nothing for this kind of scenario. When our ADC left, a comeback was unlikely but still possible. Without him, it was definitely impossible. Why am I punished for the toxicity of others? And don't give me the "it goes both ways" argument, because it should be going NEITHER way. This kind of experience ruins the fairness and the fun for 9 other players. "It goes both ways" is a very irresponsible stance to take when it comes to people that are actively ruining the experience for others.