Gnome changed some things with Gnome 3.x (which was not recently) and some people were dissatisfied with it, so they forked Gnome 2.x, created the Mate Desktop Environment and that's it. Nothing happened to Gnome, it's alive and kicking.
If I'm not mistaken, MATE is far away from being the only fork of the 2.x version.
would not surprise me, it's by far the most widely used and well known though I guess
If you're referring to Cinnamon, that's actually a fork of Gnome 3.