I find that it's nice to work with somebody and spin off on someone else's feelings. You get a little jaded by yourself.
Republicans believe largely in the market working, Democrats believe stereotypically that you've got to give people something. So why not give people a chance to let the market work for them.
Moreover, behind this vague tendency to treat religion as a side issue in modern life, there exists a strong body of opinion that is actively hostile to Christianity and that regards the destruction of positive religion as absolutely necessary to the advance of modern culture.