Why did they want to move natives to the Great Plains

The rationale was that moving Native Americans to this Permanent Indian Frontier would open up land in the eastern United States for European American settlers, while protecting them until such time as they were willing and able to assimilate into American society. Jefferson also believed that consolidating Native Americans in the Great Plains would create a barrier that would prevent American settlers from dispersing too widely.

Settlers from Europe seeking freedom also saw an opportunity in the move to the Great Plains.

Explanation:

The move to the Great Plains presented an opportunity for European immigrants to escape poverty in their home countries. African American settlers also moved to the Great Plains to start their lives as free men.