Why isn't there an option to quit before 20?

Let me preface this by saying I'm talking more about if you have afks/trolls, that there maybe should be an option to end earlier. I just got out of a game where the rest of my team decided to quit and sit at the fountain, so for around 15 minutes it's a 1v5. I can't quit, if I walk away from my computer I'll get dropped from the game. In no way is that fun, and in no way could I ever win that game.

You see this countless times, especially in ranked where someone is either trolling, or just never connected, and you have to sit there for 20 minutes, knowing full well what the outcome is. Yes once in a while you can pull off a win, but the vast majority of the time it doesn't work that way. If you want to put in some system where it only works with afk's, fine, I'll deal with the trolls, but it seems kind of a waste of time to have to sit there for 20 minutes, getting punished for someone else's mistake.

Would like to hear some feedback, as maybe I'm in the minority, or someone may have a system they could implement.