Why do Garden/Graveyard Ops teammates sometimes exit queue with me?

your teammates won't be dragged out with you as long as you are not the host of the game. As for why sometimes you get pulled into someone else's backyard, I'm not sure. The only thing I can think of, is if the host were to add all the people onto their friends list and then back out, and maybe it will drag the rest as well. I'm not sure really though. This happens to me rarely.