I really don't dislike org-mode and respect it and you are right that org-mode was first.

The point is that markdown could have todo's or virtually any other aspect that org mode supports put into it without changing the markdown standard and layer org functionality and various features on top for example todo's could simply be italic's starting with todo: so `# todo:todo hello` could be parsed as a todo entry marked as todo.

It's not that simple. The formats differ structurally. Org-mode is a proper tree - that's its fundamental basis. A tree where each branch can hold k/v pairs of metadata. Markdown is rather a flat sequence of blocks with level markers sprinkled in. Neither of that (proper tree or records) fundamentally supported in Markdown within an agreed spec - pandoc attach attributes on its own way, kramdown does it differently, etc. That's the most difficult part - there's no agreement of what Markdown is - each tool treats it differently. While Org doesn't have a formal spec either, there's no mess, because "the spec" is in the Elisp code it ships with. Even if there's fragmentation (Org-Roam, Denote, howm, vulpea), it is all contained within emacs-land.

If you want to use markdown for Agenda and calendaring in Emacs you'd have to invent a different subset of markdown, most likely poorly supported anywhere else. And if you get there, then it begets a question - why? If we already have something far better and it's called Org-mode?