Why?
Well, it's just too obvious and not even worth going into, frankly.
But we can all accept that many of these Conspiracy Theories or Legends of Yore may originate from some concrete basis; it's just that the INTERPRETATION might be wrong or 'skewed by the political agenda of the era'.
Star Gazing goes back through the aeons ... might it even go back 12,000 years to the time of the (extinct) Clovis Civilisation. A time when a meteor shower has found to have hit the Earth and had a good go at ruining whatever species were existent in that region at that time.
Scientists have found compelling evidence that a meteorite storm hit the earth more than 12,000 years ago, and is likely to have been responsible for the extinction of a prehistoric people and giant animals including mammoths.
Evidence of the meteorite’s intense heat was found on two continents. The researchers believe the huge cosmic impact triggered a vicious cold snap, which caused widespread destruction.
The international team found a substance known as melt glass, which forms at temperatures of 1,7000 to 2,200 degrees Celcius and can result from a ‘cosmic body’ hitting the earth. [source DAILY MAIL]
This may have been how somethign like the "Noah's Ark" legend came about. There might well have been an Ark or Big Boat that one Wise Man might have had his Family construct to 'save two of every local species'. There's no reason why not. Man does all sorts of wacko things when he's motivated.
And the extinction of massive animals like the Mammoth and survival of smaller species like the Cheetah make sense for the simple reason of SIZE of transported animal. No life boat can ever be big enough, in the global context, right?
Maybe "Noah" was just such a Wise Man or Star Gazer and saw that the incoming Heavenly Anomaly or Catastrophic Meteor Shower was something that would cause catastrophic flooding across the land, once those planetoids hit.