>>22837285 (OP)The real answer is that in the 19th century Darwinism and Positivism caused a lot of debate within religion. Obviously there was a rise in secularism, but within Protestantism there was the development of a liberal, modernist branch of thought. People opposed to the liberals banded together and a fundamentalist evangelicalism was formed. Because they came from diverse backgrounds, and consistency in authority or doctrine became impossible, this faction of Christians took an approach that was less concerned with theology and more militantly political. Even just recently this group was a powerful force against gay-marriage. But a string of defeats, and and aging (and dying) congregation, caused them to lose their ability to swing elections. And, once you stop being politically useful, people stop pretending to like you.
If there's ever a Protestant renaissance (I don't really care if there is or isn't), it will probably come forth from a very philosophical tradition that manages to retain some form of political utility. That would fix the original disease which ate away at Protestantism, and bring current Churchgoers into their fold.