20 years ago, I only had a dot-matrix printer, and TeX isn't really set up to deal with extremely limited positioning granularity. Certainly everything I've written in the last 15 years has been in TeX unless it's been in HTML or something which renders to HTML. But TeX can actually be kind of problematic: you have to modify the file in order to avoid generating recto and verso pages, which are inappropriate for e-readers (or, really, any presentation form which doesn't involve dead trees). And TeX documents actually often make a lot of assumptions about the form of the result which means that there isn't machine-readable available to produce other presentation reasonably.
(Not to mention that building TeX requires implementations of at least two language dialects (WEB and \ph) which aren't used for anything else on any modern system; it's easier to make an emulator for the computers that Wordperfect ran on than to make a compiler able to build TeX, although people have done both.)