I think that's more related to the non-unified, pre-DVCS patch centric model of development, and the fact that djb has better things to do/is no longer interested in developing them.

If djb would have found an interested party to accept patches to the codebase, set it up on a code hosting site, then declared "this is the main repo for continuation of djbdns/qmail development", it would have gone a lot further than just "it's in the public domain" and no other guidance.

This has lead to things like "dbndns", which are a good attempt, but definitely not a general, cross unix version solution: http://packages.qa.debian.org/d/djbdns.html