MathML dates from a time when XML was seen as the One True Way by most standards people. The fact that TeX is not based on XML was probably enough to discount i

MathML dates from a time when XML was seen as the One True Way by most standards people. The fact that TeX is not based on XML was probably enough to discount it at the time. Nevermind that TeX is more convenient to write by far, and was already strongly established as the standard way of encoding mathematical formulas.