I think if you look at the MathML standard or some example markup you'll understand. MathML is prohibitively verbose. It comes in two flavors, display and structural, and neither one is amenable to busting out equations. Even when MathML is universally supported by browsers it will still be treated as fundamentally an interchange format seldom seen by human eyes, mostly generated by systems like MathJax from human-friendly TeX.

As long as you're converting TeX math to something else, MathML is preferable only because it may look nicer rendered than an image raster from TeX.