Why do scholars try to discredit the fact that there was an African influnence in the Americas?

Why do european scholars debate the evidence that Africans predate Columbus in America by about 1300 years 800 b.c. to 900 b.c? 1311 it has already been proven that people from the Mali tribe aka Mandingo traveled to America and influcned the American Olmec Heartland ( If you debate me give me proof and evidence of why you think that Columbus or the Vikings discovered America before the Africans and for more proof on the Subject pick up Ivan van Sertima's " They came before Columbus". You will get ten points for the best answer thank you.