Whole Teams losing on Purpose?

Okay so this has happened quite a bit to me and the random(or not random) teams I play with and others said it's happened to them too but there are teams that only push mid lane and are really easy to kill once your team helps you out. I mean they don't get any build, run into turrets, and just have no real plan on winning. It's getting really annoying cause as much as I like winning, I hate easy wins more than losing bad games. Some people I've talked to think they're bots somehow but they still flee when they're health gets low. Are they just trolls or something cause these people are really getting on my nerves. And sorry to those who like those easy wins but I wished they'd stop.