It's simple, really.
They believe more in personal responsibility than shared responsibility. I live in the South, and the overwhelming majority of people I know would rather work hard for what they earn than take it from someone else without working for it. They believe that you must earn what you have, rather than simply be given it. And, they are okay with the fact that they don't have as much as others. They are happy with what they have.
I've lived in ultra-liberal and ultra-conservative parts of the country, and everywhere in between. The liberals I know are miserable. They can never be happy with what they have - they always see the grass being always greener elsewhere. They are also overwhelmingly underachievers with expectations that their slack will be taken up by "someone else."
Also, you have to take the data with a grain of salt. I live in a "poor" area by national standards - the median individual income in my city is approximately $30,000. However, the median home price is only about 2.5x. You can buy a "nice" home for $120-140k. My wife and I recently purchased a 2000 square foot home on 2 acres for $140k.
So, it's important not to confuse "poor" with "behind in the inflation race."
As far as my personal beliefs, I would rather shovel shit for minimum wage that reach into your wallet and steal your money. That is wrong, and I won't do it. So, it's not about voting in my own self interest, it is about voting for what is right.