Why build an Ark?

[Angrboda]

Because then to maintain the illusion that the Bible knows what it’s talking about, it would need to name the high ground.

By the time the Bible was written down, people of the Middle East would have had vague notions that many mountains far higher than the ones with which they were familiar existed somewhere beyond the area which they knew well or even marginally.

Given the yokelish knowledge horizon of the prophets of the omniscient yalweh, any place worth naming would open the Bible to the later question of “well the Hindu Kush, to say nothing of Andes and further Himalayas, or even Alps and Urals, were far higher, and so, what happened to people would naturally would have sought safety there?”

So shortening the period of rain and pointing Noah to a high ground where he could live when everyone else drown would open points of predictable vulnerability that would not serve the purpose for which the narrative was scripted.

I think you're attributing a level of insight and self-consciousness to these authors that they simply didn't have.