A couple of things. First, the Christian religion enjoyed a monopoly for a long time, you were either Christian, or you were in a world of hurt.

Second, the next major wave of consciousness, the rational (hypothetical-deductive) mindset replaced the high-mythic, so there was no desire or need to find a new story/mythos.

The Osiris/Horus mythos may have lasted anywhere between 3000 and 5000 years, but when it was replaced by Christiainity, Christianity's insistence on its historical/literal value was actually one of the reasons it did survive the others. So in that sense, I could see the dread of engaging in speculative theories such as this. Ultimately, I think Christianity could survive it, even become a much deeper spiritual system since the cultural background of the West really is Christianity as opposed to Buddhism, which has done a good job replacing the mystical insight of Christianity. But, if Christianity developed a more mystical practice by letting go of its insistence on historicity (which I believe holds it back by continually having to deal with pests like me), its cultural identification in the West would benefit it more and people wouldn't seek out the deeper Eastern approaches.

By the way, when I say "deeper approaches", I don't mean to imply that everyone in the East (Buddhists/Hindus/Taoists, etc.) don't have the greater portion of their population that believes in the mythical stories as well, they absolutely do. It just that the traditions there don't stop there. They learn that the stories attributed to the Buddha and Krishna and such are meant as teaching tools, and that real spiritual development is a deepening of consciousness. I think many people in the West have this idea that all Buddhists in the East are these meditating masters, when in reality, they have just as many religious stories they believe are literally true as well.

-TC