And while bringing Emacs/Vim up to acceptable GUI editor standards might be possible (MacVim does an alright job of this), I'm guessing that a lot of the head Emacs/Vim people would be against it, and wouldn't want to merge it back into mainline. That would leave FB having to maintain their fork of it, and splitting mindshare, etc. Atom doesn't need that much work, and it's easier to maintain a plugin than an entire fork.