Why do we get punished for AFKers?

I'm actually so frustrated. We just had a really competitive game back and forth for the first 20 mins or so, until our graves decides to call it there, and just left, the entire game went on for 50 mins, where we just ended up getting pushed back, but shouldn't the system at least realise that someone has been afk for a large amount of time and not decide to punish the rest of the time by loosing over 20LP? Also can we have solo queue back thanks, getting tired of being put against teams of 3-4 people. rant over
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