This site used to be one of my favorite examples of content over presentation. What happened?

Youngsters.

I'm not sure what you mean by 'youngsters'--c2.com (and the associated wiki) are still maintained by Ward Cunningham, and the effort to rewrite the wiki[1] is hosted under his GitHub account and appears to have been his decision. It appears to have been motivated by a desire to "federate" the wiki, though I'm unclear on what exactly this vision entails.

[1]: https://github.com/WardCunningham/remodeling