To me what was most surprising about Dwarf Fortress, given the complexity, is that Tad didn’t use git or any other code repository until more recently.
Why would that be surprising? For a single programmer working alone Git is an incredibly complicated tool. P.S.: A lot of you are confusing "complicated" with "difficult".
If I switched to working with a team I'd definitely use git. But for just me, cvs is all I really need. The most complicated thing I do is probably tag a release or revert to a previous revision of something, which is pretty rare.