Political Cartoons

Because they're being used. First they are threatened that their morality is under assault (which is nonsense, but hey), then the GOP comes riding to their rescue. The result:

While Christian conservatives with high incomes are more likely to vote for Republicans than their poorer counterparts, evangelicals "tip" to the Republican Party at a much lower income level than do other voters—about $50,000 lower, according to statistical analysis. Put another way, an evangelical voter with $50,000 in annual income is as likely to be a Republican as a nonevangelical voter with $100,000 in annual income. In a country where the typical household income is around $50,000, this is hug effect, and it means that Republicans attract far more support from lower-and middle-class voters than they would otherwise.

(Jacob S. Hacker & Paul Pierson, Winner-Take-All Politics: How Washington Made the Rich Richer—And Turned Its Back on the Middle Class, Simon & Schuster, 2010, pp. 148-149, I underlined for emphasis.)