Some people I know literally share LaTeX math in emails and chats and assume my head has an internal LaTeX-compiler to understand it (usually I do). I guess this means people are really accustomed to writing maths in one go in LaTeX -- it's like the pseudo-code of maths.

Why? It is almost as old as LaTeX.

Not everyone enjoys programming their documents and visual editors for LateX written in Motif were the first ones to become available.