People tend to naturally gyrate toward what is familiar, and also I have noticed that on message boards there seems to be a rather strong tendency to lean toward "camps" as in Derek's fan camp and/or Maks's fan camp.
Sometimes, there is even a dilemma when the poster likes the pro but doesn't particularly care for the celeb, or the opposite occurs, and the poster immensely likes the celeb but doesn't care for the pro.
I also think that in some way that may be hard to quite nail down, pulling for the pro make this whole experience more enjoyable. It adds a little something.
All of this, of course, really has nothing to do with dance in and of itself - that's incidental to the discussion!