Being afk for 5 minutes is an eternity in a Ranked Match. A game you were winning can turn around for the other team drastically in that timeframe. Couple turrets, a dragon, an ace, maybe even an inhib. I actually think they should reduce the time for afk in ranked matches. I've had a lot of people who afked a few minutes before we surrendered or lost and in postgame their name wasn't red, so the system didn't even register them as a leave.
When it rains pretty good, the power in my little town has been known to flicker or even shut off for a little while. So I don't play when it rains. When I hear thunder and I'm in the middle of a game I panic. Simply not starting a game after 9 or before 10:15 or so is a lot easier to work around than never playing when it rains. It sucks for you, but it sucks even worse for your teammates.
Being afk 5 minutes late game can turn a win into them blowing up your nexus just that fast. It's happened to me twice this week. Winning a game then someone dc's 40 minutes into the game, teamfight, ace, loss. Did they intentionally dc, no they came back.....just in time to see the nexus blow. And it didn't even take 5 minutes. 5 minutes early game is a little more forgiveable if your team reacts appropriately and covers your lane or you are the jungler. Late game it just puts your team down a man at a time when teamfights are frequent and people have items built.