MathML is supposed to be generated by software and rendered by browser. You're free to write LaTeX JavaScript convertor which could convert LaTeX to MathML (and

MathML is supposed to be generated by software and rendered by browser. You're free to write LaTeX JavaScript convertor which could convert LaTeX to MathML (and probably those convertors already exist). Nobody is going to ask users to write MathML, just like nobody is asking users to write proper HTML. Supporting MathML instead of LaTeX makes sense, because it's machine-readable language which is easy to generate and parse. HTML uses XML-like notation, SVG uses XML notation, so it only makes sense for equations to use XML notation instead of completely different language.