>for an obscure reason known only to its author

It's, in project's words, simple calculator-style syntax (can also call it simplified LaTeX subset or that ad hoc math syntax used in emails but standardized) made to easily embed math on web pages by converting to MathML, with its existence predating MathJax by few years (and even MathJax's predecessor, jsMath). It was never meant to be LaTeX competitor.

With last point, have noticed people most often use this xkcd strip opposite to what it means. It's about when, for a particular use case, one standard/tech/whatever tries to replace all others rather when one standard/tech/whatever attempts to fulfill a distinct use case.