.md files are mostly (only?) used by engineers. Why build and maintain a second app when you already have something that does the job sufficiently?

It would be mostly the same code. But loading Xcode is overkill when you just want to edit a markdown file.

Just use a plain text editor.

I like WYSIWYG editing.

What if you used something like VSCode if you don't like Xcode?

Or one of the many many others that exist? A quick google yielded this one for example: https://stackedit.io

Be resourceful :-)

You don’t love it when you open a file that is randomly associated with Xcode and you see that icon start to bounce?

As bad as accidentally clicking on a mailto: link and watching Mail.app spool up.