I think it was a combination of it being new at the time and there being a lot of kids playing it. Older teens/young adults often tend to not want to play with young kids. I remember everyone used to complain about, and make fun of kids (aka twelvies) playing COD. I seem to also remember people making fun of Minecraft because it was for kids. As for why it stopped, I think it just got old. The hivemind moved on to hating something else. People grew up a bit, the 12 year olds are now 17? (bloody hell time flies).