Christians: Why don't you accept that not everything in the Bible is necessarily the word of God?

I already accept that. I think of the Bible as the foundational library of Christianity. You wouldn't expect a library to have no books that ever contradict each other once. Moreover, the Bible is inspired in the same way a poem is inspired by a sunset. It records authentic encounters between humans and the divine, and as you say, it's also a product of the culture of the times.