The point is that MathML is easier to translate to then many of these other languages. I wrote a language my self a few years ago that translates to MathML (https://runarberg.github.io/mathup/) and MathML was an absolute joy to target.

In mathup I included a second target to update the DOM directly .toDOM() and .updateDOM(oldMathNode) instead of .toString(). This would have been quite difficult if there wasn’t a nice mapping between the language and the DOM nodes. By implementing math in MathML browsers have made it easier for us software authors to write these other languages that serve different purpose then LaTeX. Our users benefit from this proliferation. Ultimately they don’t need to know which language is the native one, because all they write is:

    <math-up>ln x = int_1^x 1/t  dt</math-up>

And let the library translate to MathML for them.

I think UnicodeMath [1] is really interesting and approachable and is a standard that Unicode themselves have been keeping an eye on/helping maintain. It takes advantage of the richness of Unicode in interesting ways that makes the formula encodings in plain text better resemble their formatted counterparts. (You just have to forgive that the standard originated from the Microsoft Office team.) The interesting thing to me that UnicodeMath partly implies is the idea that math formatting could be considered similar to "regular font rendering" in a similar way to how ubiquitous emoji have become.

[1] https://www.unicode.org/notes/tn28/UTN28-PlainTextMath-v3.1....

I think the LO Math formula language is nearly an exact implementation of eqn. I prefer eqn to LaTeX because it is easier to remember/write/read, but complex equations tend to take some fiddling to avoid ambiguities.