Same reason that people believe(d) in Dragons, worshiped Gods, deferred to Royalty, carried out blood-lettings, danced around Maypoles, burnt witches, feared comets and believed that there was a race of one-legged people who lived their lives on their backs sheltering from the sun under their massive feet (http://en.wikipedia.org/wiki/Monopod_%28creature%29)

Seriously. The olden days were whacked out as fuck. For every "That's just so crazy it might be true" story in the Bible or otherwise 'respected' ancient texts there's a thousand "Ok, no, that's just fucking crazy" story. No significance is to be derived. These things are not and were never true.

They had a pretty good excuse though - they didn't have easy access to the ridiculous amount of amassed knowledge we all know have access to. It's easy to call them stupid, but in reality most of us probably would "go along" with whatever was believed by most people at the time... however if you believe it now? Yeah, you ARE stupid.