Afk's and rage quitters in ranked

Why is the entire team penalized for one player disconnecting at minute two, im a support main and i was playing ranked with a friend and we get into a game with an ekko midlane, after his first death minute two he rage quit the game. I got my adc fed, she ended with 26 kills as trist but we lost due to the jungle having to stay midlane because our ekko decided to leave. why is there not some kind of program to prevent this or atleast dumb down the results of losing 21 lp due to a rage quit. Isn't ranked supposed to use your mmr based on how you play not how long your team stays in a match