Comment by GiovanniP

I think it is fair to point at a paper where Van der Hoeven argues in detail in favor of the WYSIWYG paradigm:

J. van der Hoeven. GNU TeXmacs: a free, structured, wysiwyg and technical text editor. In Daniel Filipo, editor, Le document au XXI-ième siècle, volume 39–40, pages 39–50. Metz, 14–17 mai 2001. Actes du congrès GUTenberg.

Reproduced at https://www.texmacs.org/Data/TeXmacs.pdf

For why so few people use TeXmacs, it may be that it is because few people believe that it is worth trying, as one would not expect that it works so well :-)