Goals aren't results. It was a goal for Markdown to be simple and universal. It is not a result.

You may be struggling a bit because you are reading some sort of moralization into the statement, some sort of emotional judgment, but there isn't any. It is clear that there does not exist a function that takes a span of "Markdown text" in and emits an abstract syntax tree that everyone agrees upon [1]. That's a fairly mathematical way of putting it, but even from an engineering point of view, the differences matter. Very quickly. It's not like you need to reach deep into crazy syntax to get to real, concrete disagreements between systems, you can hit problems with something as simple as

    "_hello world _"

between the systems where they will do substantially different things.

There are literally dozens of markdown formats now.

How we got there, why such a thing exists, as interesting as those questions may be none of them change the reality on the ground. There is no universal markdown to be appealed to. The closest is CommonMark, and that explicitly exists precisely because there was no consensus in the first place. If markdown was a format, CommonMark would never have been created.

[1]: Nor does its inverse, which at times is more frustrating to me than this. I have in mind what I want to do and either can't figure out how to do it or it simply can't be done.