That looks like a different type of writing, perhaps research or business writing. Wordstar like editors that bring simplicity and a distraction free environment are best suited for creative writing.

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.

A large fantasy adventure could easily have supporting documents with cities stats, characters, races, maps etc.

It could have, but George R R Martin famously uses Word Star and he surely has all that.

Then again he's also about a decade late with the next book

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.

My point exactly; sci-fi you even more need to refer to accurate statistics whatever they may be.

Unless the fleet travels at the speed of plot.