FreeBSD Handbook Improvement Survey 4 years ago
Perhaps it's not as large as you think, relatively speaking. If we take a look at bugs.freebsd.org, it seems that many bug reports are opened and left to rot for years. The documentation section of the tracker is no exception.
https://bugs.freebsd.org/bugzilla/page.cgi?id=showreport.htm...
Seems to be getting worse with time too.