I have noticed that Republicans seem to be rather self centered. Very rarely do they put cause ahead of personal ambition, unlike Democrats. See NJ 2002 and MO 2012 for two prime examples from each side.
I suppose what surprises me is not so much that Richardson is still running but that anyone is supporting him. Although, I suspect in reality, Richardson's support is not so much from people who think Poliquin is too liberal (as Richardson does) as from people frustrated by both major candidates.