I've found trying to find a distraction-free editor a distraction in itself. I'd bet money that most authors using an old word processor had some external reason to use it (cost, availability, editor compatability) and just stuck with what they know.
GRRM could use clay tablet and it wouldn't make any difference on his output.
If you want output, Stephen King has used many processors, he doesn't care aparently as long as he can focus. Brandon Sanderson uses Word. The tool doesn't seem to matter.