It was a rhetorical question. I understand how TeXmacs works.

It does use LaTeX: it contains a usable LaTeX importer/exporter. Yes, the importer and exporter aren’t perfect, but they are used in a nontrivial capacity nevertheless. LaTeX is such an integral part of the research workflow for so many academics that leaving it behind entirely is not an option. So instead many people use TeXmacs to generate LaTeX for submission e.g. to a journal. To me, this means that it is a LaTeX tool. Maybe this is not exactly the intended use case, but here we are.