Because something as basic and necessary as the Trinity is not clear.

Because Paul teaches all the true churches of God have women who pray with their heads covered, contrary to what we see.

Because the Bible gives a creation story that doesn't match scientific evidence or reveal dinosaurs.

Because there are entire chapters in Leviticus that suspiciously read like a combination of a medical textbook and supserstition when dealing with leprosy. Why only leprosy out of thousands of diseases?

Because the chapters on genealogies, the tabernacle, the priestly garments, and the temple are totally irrelevant to living as a Christian.

Because the Bible doesn't clearly address whether Christians should keep the Sabbath, when the Old Testament said Sabbath breakers should be executed.

Because of the historical inaccuracies.

Because of the commandments to take slaves, and kill children.