You make it sound as if you write HTML5 by hand when entering content in web pages. Do you have the same complaint for SVG diagrams or HTML tables, which are even worse for writing by hand than MathML?

I hope not. The key gain here is that the syntax used for mathematics in HTML needs to be easy to integrate in the web platform of 2021. Can you still use the DOM with MathML? Yes. Can you naturally interleave it with other HTML elements to create multi-modal constructions? Yes. With diagrams? SVG+MathML is possible, yes.

Indeed it is designed for technologists, solving a problem on the world wide web, as well as in other structured formats. And no, no one is asking mathematicians to type XML or HTML by hand in 2021.

An author can keep using latex, asciimath, Word or OpenOffice, MathType, MathQuill, or even Mathematica/Matlab/scipy syntax, as they've done until now. And then have their toolchain of choice prepare MathML to be served on the web, (or epub ebooks, etc), in a uniform manner understood by all vendors. Mere mortals can then finally create web apps that can natively access the math, without writing half-baked tex parsers that have hundreds of awkward and undocumented special cases.

TeX syntax has no path to richer integrations into the web platform and keeps mathematics out of reach for all modern ecosystem trends. I certainly think MathML can still be improved quite a bit - mostly by making it smaller and simpler, so that anyone can pick it up in an hour and write a new app in a day.