Probably because it can be difficult to get the next rank(knowledgeable) and those ranked novice out number everyone else.I find the ranks to be ppointless being as they are based on opinion of the people who rank.
People are rarely ranked according to their true depth of knowledge and being ranked as said above can be difficult considering only those ranked Adept & Knowledgable can perform rankings. I tend to pay more attention to how one acts and the information they present on the forums rather than their rank when judging their wisdom.
There are currently 30 covens available in which someone may attain the Priest or Priestess position. Since there are 2 leadership positions for each coven it would mean that there are 60 available spots. In my experience of being on this website, I've only seen around 20-30 people ranked as either 'Knowledgeable' or 'Adept' since the ranking system was put into effect almost 2 years ago. Of course there are members with those titles that I have yet to see, but even so, there simply aren't enough active members with such a title to fill all, or even the majority, of the positions.
And thus, that leaves us with members ranked as either 'Novice,' 'Beginner,' or even 'Fluffy,' to become the leaders of the covens. As 'Novice' is a title easily achievable, you will find it on many profiles.
But as the members above me have said, the rank you have is nothing more than a colorful box on your profile description. The true level of your knowledge is what really matters, and the true level goes largely unseen by many.