Was there any particular reason why these areas were more Unionist?
Most of it is miserable mountain country full of a people who were always hostile to the culture of the rest of the south.
Unfortunately they are now very similar to the rest of the white rural South, at least in terms of how they vote.
Indeed culture too (though its not quite as monolithically one "country" culture as media portrays it), which is generally more the result of the degeneration of the rural south (or its overwhelment by crude suburbanites, who pathetically imitate the ways of southern culture) than much change (except that created by modern technology) among the hill peoples.