Because once an indentured servants time is up, you have to let them live their own life, but if you have a slave, you literally own them and keep them until they die if you choose to do so.
In 1839, a group of Africans took control of a Spanish ship called La Amistad that was bound for a port in Cuba where the Africans were to be sold as slaves. After seizing the ship, the Africans demanded to be taken back to their homeland, but were tricked by the ship's navigator who set a course that took them along the coast of North America. La Amistad was eventually captured by the United States Navy, and the Africans were held as pirates. Though they were almost taken to be sold in a U.S. slave market, a court case arose regarding whether they could actually be considered slaves. Abolitio
Based on the tapes from the oval office, Richard Nixon felt that because he was president that he was above the law. This meant that the normal laws of the Untied States did not necessarily apply to him.
However, this was not the reality of the situation. In the Supreme Court case Nixon vs. United States, the Supreme Court ruled overwhelmingly that Nixon was not above the law and had to hand over the tapes to the court. This ultimately resulted in the resignation of Nixon.
I think that courts favored Americans over immigrants because of nativism- the belief that a nations people are better than another country's people
