The reason is actually fairly simple. There is a strong Palestinian diaspora political presence in the United States that did not exist 20 years ago. Obviously, Palestinians have been under duress for a long time, but they have had little representation in the United States.
During the last 20 years, there's been a significant wave of Palestinian immigration to the United States that has found its voice. This voice was amplified on campuses across the U.S., and here we are.
African countries, on the other hand, don't have that same diaspora in the U.S. I suppose one would expect them to in Europe, where there is a significant presence, but, as the map sort of indicates, they are scattered and have diverse interests. They don't have a unified voice through which to say, "HELP!"
As for Trump. He has no ideology. He is not left. He is not right. His ideology is insanity, and his platform is hate.
So that is not part of the discussion I would have with anyone. People who are upset with Biden over policy at least have the right to yell at him about it. They may not in another couple of years if Trump, a convicted felon, serial sexual assaulter who was legally identified by a New York State judge as a rapist in his civil rape trial, and bonafide racist who despises the Africans on the map with every inch of his soul, finds a path to winning the election.