Interesting question.
Perhaps because they still see themselves on the side of "the little guy", rather than on the side of the big corporate giants that they identify with Republicans as genrally supporting.
I just thought it funny that the Blue Dog common ethic was "fiscal conservatism and accountability", which assumes that the rest of the Democratic Party DOESN'T support those values.
Democrat is now going to be synonym for “Aristocrat.” Republican will now be known as “The public” who will not be part of the party therefore part of the peasantry.