The force that kept Christian books stores open was conformity. People of a certain branch of the faith expected to visit these stores and know that what they bought reinforced what they already believed. As conformity began to lose its grip, the bookstores that used it for their own success found sales dropping.
Conformity is also hurting church denominations. The faith has had a history of top down authority. The Bible is an authority. The denomination and then the preacher/priest are figures of authority. All this to ensure conformity.
The internet has hurt large parts of the retail system and religious book stores are falling by the wayside like Sears and other retail stores. I always think of churches themselves as retail institutions selling what was provided them by manufactures/wholesalers, the seminaries and central offices of denominations. Now, the retail shopper for religion has other stores, their computer, where she can find exactly what she wants. The conformity demanded by the denomination has sprung leaks.
The traditional Christian book store would not stock a book that argued gay marriage is unaddressed in the Bible. Probably it would have a tough time with books advocating abortion rights or even birth control. This conformity based business model is now failing.
One commercial aspect of the faith that does seem to be doing well is the Christian firm, Hobby Lobby. Some local bookstores that sell such “collectibles” are doing OK as well.
Another term for our growing diversity of thought is post modernism. It continues without pause.