I haven't used FreeBSD in quite a few years, but I'm sad to hear it's no longer what it was :-(
Looking at the source it looks like they went from the obscure SGML to ... some obscure XML. The entire thing looks horrible and a pain to edit, so I'm not surprised that few people contribute (including the OP).
While they are less powerful, markdown, restructured text and other simpler markup languages are much more productive to work with. They are easier for beginners to understand, and the markup is sufficiently lightweight for most of the common cases that it doesn't interrupt your train of thought while trying to think about how to best describe complex technical details.
Which isn't to say it's not very good at what it does, just that I can't see a compelling difference over DocBook or HTML.