Because the people settle there. The land was “empty”, like it was “empty” for the settlers in the Americas.

settler: noun a person who moves with a group of others to live in a new country or area. “the early European settlers in America were often fleeing from religious persecution”

synonyms: colonist, colonizer, frontiersman, frontierswoman, pioneer, immigrant, newcomer, incomer, homesteader, habitant, redemptioner, squatter