I'd argue that it's hard to parse because it's so open-ended. E.g. Markdown is only one example of how to structure textual data in plain-text with additional "syntax".

Imagine it wasn't decided on Markdown. E.g.: I don't use markdown when making plain-text notes. I make it all hierarchical and indent using "- ". I.e. headings are top-level, sub-headings are indented by one, and so on. Eventually, you realize that all things can be represented as just lists of nested lists. No need for some arbitrary "heading" type, just nest it all based on the concept.