Obviously, you don't know me well. Feel free to offer rebuttal, I'm not afraid of the discussion.
There are various reasons, but fundamentally it'll come down to the fact that Huckabee was one of the three men who raised his hand in
this video. Quite simply, if you are willing to say in front of a national audience that you do not believe in evolution, I do not think you are qualified to be president of the United States. To me, this is worthy of the same reaction we'd have if one of the candidates raised his hand if asked "who believes the sun revolves around the earth."
His later demurrals that it isn't important whether he believes in evolution because he isn't asking to write high school textbooks just makes it worse since it would appear he has no understanding of the role the president plays in fostering policy in the executive branch. His later comments that he believes god created the universe "but he doesn't know how long it took or how it happened" is a better answer but then suggests he answered the question in the video without understanding it since believing in God does not necessarily require not believing in evolution (just ask the last pope and the vast majority of scientists).
So, right there, I am completely off the bandwagon.
Then there's the fact that it appears he is a social conservative but a fiscal progressive (both Republicans and Democrats tend to be fiscally progressive they just disagree on which problems need progression) which is, in my opinion, the worst combination of stereotypically Republican traits (this part, admittedly, is mostly from an NPR profile but based on the disqualification above I don't feel the need to poke into details too much more.