Why is losing a 3v5 still treated as a reflection of my skill with regards to LP and MMR?

Leaverbuster already detects that they have been afk, and they remain afk when the game ends, so why not lessen the blow of the loss somehow? It is hard for me to believe that "preventing abuse" is a valid reason to skew the system so heavily. Two games in a row I've had at least one leaver or dc or ragequit. That means that I have to win 3 additional games to progress beyond where I was, for something that was entirely out of my control. It doesn't seem like a positive or fair system to treat these games the same as a 5v5 which was lost by misplays. In the interest of fairness, LP and MMR should also be negatively impacted by a leaver on the enemy team. I just feel like there is a better system out there than just ignoring the enormous imbalance a game with a leaver or afk or ragequit creates.