If you are black, you should know why not. I suppose you are a recent arrival to America.
The U.S. was home to the former slaves. Most of them did not want to go to Africa. It was an alien land to them. Different customs. Different foods and huts for shelter. Few Western machines. Not what they were used to. Tribe and clan based cultures. Think of Britain. English, Irish, Scots, Welsh, Channel Islanders, Manx, etc. They may look alike, but they are different. Same with Africans, and the Africans didn't want the newcomers. Who knew what tribe their ancestors came from? They could not be integrated. Canadian winters had been hard enough for the escaped slaves to bear. Many of the returned south after the American Civil War ended and slavery was abolished by a constitutional amendment.