TeX is not a general purpose typesetting system: its core proficiency is in typesetting long texts with lots of math. In that it doesn't have any competition, I can imagine several reasons:
- Donald Knuth was smart. He did amazing job with, for example, spacing in formulas.
- Math notation changes across periods of time like centuries. There's a limited set of features that is necessary and thus no market for new typesetting systems.
- Network effects. The only purpose of paper is to be read. Most papers advance on some others' research and are using their notation. With TeX you're sure you get the same fonts and the same spacing, and you have a technical ability to copy complex formulas from their papers.
- In TeX it's trivial to define new macro, it's usually easy to say what a simple macros does from its definition and there many standard macro libraries. Any GUI-based system would likely make this process much less transparent.
While the drawbacks you quoted are real, it's much easier to look around for a decent editor/GUI shell built on top of TeX, of which are many, than to typeset in a different language. If you're into math, and want your articles to be preserved for decades, that is. For the general purpose typesetting, again, the programs you mentioned could well be a better choice.
