Absolutely true.
I would posit that most people writing LaTeX aren't writing up papers in it either (Most journals prefer or require Word these days).
ConText isn't just for books though..it's great for any sort of thing with formatting...like, say, a resume.
what exactly do you think they're writing in it then? business cards?
as the other commenter said: publishing across math/physics/cs i have never seen a journal not prefer latex to word. and while ieee accepts word it most certainly prefers latex:
https://www.nature.com/srep/author-instructions/submission-g...
"Whilst Microsoft Word is preferred we also accept LaTeX, or PDF format."
In general Word has eaten up everything that isn't hard core math.
(PS: All the IEEE journals accept Word.
I know that for some journals (osapublishing.org, which is optics so engineering/physics) this came at a time when they moved all their content to be accessible as html. I remember reading somewhere (maybe in their style guides) that they said that word allows them to extract the relevant information more easily, so I suspect that MS made some sort of publishing toolchain for this usecase and the publishers lapped it up.
I know that a significant portion of colleagues still prefer to write their documents in latex, and the journals still accept them.
it’s probably true that most papers aren’t written in LaTeX but I’m confident most people writing in LaTeX are writing scientific papers.