I believe the answer is: they had been born in the United States and considered it home
Despite the horrible treatment that they received, they still see United States to be the environment that they are the most familiar with. On top of that, a lot of them believe that the amount of job opportunities in united states far exceeded those in African continent.
Remember the conquistadors were in search of gold on the Native American lands. They probably treated them harshly because they were greedy and wanted to exploit the riches of the land so they wanted the Indians gone.
Beringia was a land mass that once linked Siberia and Alaska.
Southern Democrats found loopholes in several different laws that allowed them to limit the rights gained by former slaves during the era of Reconstruction.
A perfect example of this would be the requirements/obligations put in place to limit former slaves from voting. This included the development of literacy/citizen tests, poll taxes, and the grandfather clause. The tests given were often near impossible to pass, the poll taxes were ridiculously expensive, and the grandfather clause stopped individuals from voting based on whether or not their grandfather could vote. All of these laws lasted several years before their repeal.