I think, part of the reason why The Dreaded Terminal is still so prevailant in the perception of Linux is that it's just SO MUCH easier to write manuals for.
I mean, it's way more efficient to say: "run `apt install firefox` to install firefox" than "to install firefox, open the software center [screenshot], search for firefox [screenshot]", select firefox in the application list [screenshot], click install [screenshot]".
The results are the same. Why waste more time drawing a comic book when you can tell a person to just type one line in a box?