Why Would Humans After Hundreds of Thousands of Years Suddenly Endeavor Megalithic Building & Worldwide?

Isn’t it odd that humans after supposedly hundreds of thousands of years decided to suddenly build huge megalithic structures only about four thousand years ago, and all over the world at that? And isn’t it remarkable that four thousand years ago aligns with the biblical chronology of the repeopling of the world after Noah’s Flood as outlined in Genesis 10?