As you can see, country is the most "upbeat and conventional" genre of music. A preference for "upbeat and conventional" music is negatively correlated with "openness" and positively correlated with "conscientiousness," and so, as you would then expect, self-described conservatives tend to like "upbeat and conventional" music (more than any other kind), while self-described liberals tend to like everything else better.
Again, those low in "openness" are less likely to visit other countries, try new kinds of food, take drugs, or buck conventional norms generally. This would suggest that most conservatives aren't going to seek and find much intense and meaningful emotion in exotic travel, hallucinogenic ecstasy, sexual experimentation, or challenging aesthetic experience. The emotional highlights of the low-openness life are going to be the type celebrated in "One Boy, One Girl": the moment of falling in love with "the one," the wedding day, the birth one's children (though I guess the song is about a surprising ultrasound). More generally, country music comes again and again to the marvel of advancing through life's stations, and finds delight in experiencing traditional familial and social relationships from both sides. Once I was a girl with a mother, now I'm a mother with a girl. My parents took care of me, and now I take care of them. I was once a teenage boy threatened by a girl's gun-loving father, now I'm a gun-loving father threatening my girl's teenage boy. Etc. And country is full of assurances that the pleasures of simple, rooted, small-town, lives of faith are deeper and more abiding than the alternatives.
My conjecture, then, is that country music functions in part to reinforce in low-openness individuals the idea that life's most powerful, meaningful emotional experiences are precisely those to which conservative personalities living conventional lives are most likely to have access. And it functions as a device to coordinate members of conservative-minded communities on the incomparable emotional weight of traditional milestone experiences.
Country music, the most conservative of genres: