Mastery trolls in Flex Ranked

I've seen this a few times. I enter a Flex Ranked game with a team of 3 and run into a team that has no intention of winning, just ranking up kills. So by 10 mins in, they are wrecking our team, but instead of killing towers they just run around and gank, dragging the game out. Are these smurfs trying to get masteries?

Ranked flex is a good option when you have 3 people who want to play together. What's going on here and can Riot fix it?