Because it was rough time.
1. migration led to populating the world from people moving from place to place, mainly after the Ice Age when the ice melted (it connected Asia to North America). This connection of ice led to traveling and eventually creating different civilizations all around the world.
2.Benefits of permanent settlement: solid resources that can be reached at any time. stronger homes to live in. crops growing for months. Benefits of nomadic settlement: travel following seasons, so there will always be resources that line up with the weather. there's no piece of land that's "territory". following herds of animals means it's a constant food source. following where rivers flow eventually leads to lakes (salmon).
You got to look it up. i am sorry i wish i could but there a whole side on it.
