Why isn't HTML more relevant outside of the web?

Question

'relevant' in terms of more popular and wide spread as a format.

Avtomatk · Accepted Answer

XML (the superset of HTML) is used to create graphical interfaces in android applications... And there are currently many applications developed in electronjs for this same need: Develop graphical interfaces with HTML and CSS

phillipseamore · Answer

Where do you draw the line, that it's actually written as HTML or that it uses HTML/DOM for rendering?
Most apps built with Electron, and similar, run with HTML (you can argue that it's mostly JS, but it's all rendered in the HTML DOM).
Many STB's and modern TV's run some kind of HTML/browser engine. Some graphics engines for TV broadcasts. Plenty of kiosks and digital signage.

timonoko · Answer

Epub is just zipped html. In other words, html is everywhere, you just don't know it.

PaulHoule · Answer

Like people might distribute HTML files on a CD-ROM or something?