Atlassian products tend to make me SO mad in this way. Confluence, can I just use markdown? No! Forget that I used it in so many other places. Oh but wait, someone may have built an importer... try to get that installed.
Confluence used to use markdown and wysiwyg, and about 5 years ago abandoned markdown to reduce development costs. They have a lot of non-developer users using Confluence, who aren't good with things like markdown. Our shop didn't like it, of course, since we were all capable of markdown and wysiwyg is never actually wysiwyg.
I could be wrong, but I think it used textile (I believe Confluence predates markdown). I'm not sure it matters a whole lot, but if you wanted markdown it's likely you would have felt underwhelmed with textile.