There is no reason for not listing a site. Not listing is a non-event, it doesn't need a cause.
Listing a site is an event. It requires an ultimate cause and a proximate cause. The only acceptable ultimate cause is "site contains significant unique information". The proximate cause is "an editor was building categories and noticed the site."
I don't know what subjects you've been building sites on. I do know, however, that they weren't the subjects I've been looking for content on.
So who's focusing on the wrong subject? You, or the ODP editors?
The question is meaningless. Everyone's working on what they think is important. And the results are on the net for whoever else is interested.
There may indeed be no editor actively looking to build up the South African categories--nobody really tracks editor activity that way, so we really don't know.