On that note, why are all the editors different in their system? Between Jira, Confluence, and Bitbucket, each one has its own edit box, its own markup in there, and none of them are wildly pleasing.

On top of that, one thing they have in common is it takes 5-10s to load and 5-10s more to save any page (their hosted).

They're headed(ish) in this direction. In both Jira and Confluence, the newer editors support Markdown keystrokes that translate into a wysiwyg view. Jira is currently a mess, though, because it has a random mix of new editor and old wiki-style markup.

Once you get used to markdown in something like, say, Trello you really feel it when moving to something without like, say, Monday.

A team of engineers may prefer to spend inordinate amounts of time managing an internal docs project just because confluence doesn't do markdown :|

I think it's a deliberate (and, in my opinion, poor) business model similar to mobile app stores: Atlassian has a small army of plugin developers who sell their plugins for the platform (and plenty of Markdown related plugins for this purpose, for example), and Atlassian takes a big cut of that (I think something like 20%).