180 million monthly users is a significant portion of the world's population. I'm not sure to what extent MathJax is cached, so it's possible that these are not 180 million unique users. On the other hand, this does not include all those self-hosting MathJax, using KaTeX or just using server-generated images (for example Wikipedia†).
†It's possible to force Wikipedia to use native MathML (which, at least on Firefox, looks really nice) or MathJax, but it's non-trivial.
https://bugs.chromium.org/p/chromium/issues/detail?id=6606
https://bugs.chromium.org/p/chromium/issues/detail?id=152430
https://wpdev.uservoice.com/forums/257854-microsoft-edge-dev...