Because the bible is clear.
I beg to differ. The bible is far from clear. If the bible were clear there would be no questioning of debate. The authorship of the Bible is GOd, but the reproduction and interpretation of the Bible is that of both corrupt and imperfect man. Perhaps the following best sums it up:
"God wished difficulties to be scattered through the sacred books inspired by him, in order that we might be urged to read and scrutinize them more intensely, and, experiencing in a salutary manner our own limitations, we might be exercised into submission of mind." (Divino Afflante Spiritu, 45, cf. At. Augustine)