Elo isn't nearly accurate enough to measure a players skill. Just by the process of getting matched with your team, you have 4 other variables you can't control. It's really not fair that we have to lose elo for being matched with players who feed and its really not fair how other players with much less skill can gain elo just for a lucky streak. At 1700, most players know what they're doing and won't make easily avoidable mistakes. But once you're in the 1500s, all hell breaks loose. It's almost impossible to get out of it just because of the players in there, the leavers, the feeders, and the trolls.
I'm pretty sure riot has some kind of system used to match you with certain players depending on whether or not you've been reported. Thus the message displayed at the start of the game. They don't realize that it's a neverending cycle? You match players with worse teammates and they just tend to grow more and more verbally abusive.