The story of Noah' s Ark - or - God is dumber than you.

[Angrboda]

Much of the old testament never happened and quite possibly wasn't consolidated until during or after the exile. As such, it makes more sense to see these stories in the old testament as foundation stories, mythical tales of the beginnings of their people which helped to give them an identity that was eye-catching enough to stick in the mind and hold them together as a people, even though many lived scattered in foreign lands. They believed it literally because the intent was for it to be believed literally and the stories were promoted by the culture and its leaders as literally true because that addressed the pressing need for cohesiveness among exile and post-exile Jews. This idea that it was seen as allegory, and that only the simple schmucks took it literally is a later invention intended to try to remove some of the egg off the face of believers. Much like reformed Islam, which consists of a bunch of retconning to try to deny that Mohammed was a murderous and lawless asshole, the Jewish myths served a social purpose, and that purpose required that they be believed to have happened.