Tbh, we're not.
We're mostly just hated in the U.S. because of the troubled history with White America and the competition over space/resources/jobs with certain non-Black minorities.
But, outside America, we're rarely hated like that. I traveled to Latin America before and, over there, we're seen as Gringos just like White Americans. And the biggest stigma down there is towards Indigenous people, local Afro-Latinos, or poor migrant Latinos from neighboring countries.
Also, across the world, there's more hate when it comes to local Indigenous people(First Nations in Canada, Maoris in New Zealand, Abos in Australia), national/regional rivalries(Japan vs South Korea, India vs Pakistan, Nigeria vs. Ghana, Western Europe vs. Eastern Europe, Israel vs. Palestine, etc.) as well as migrant issues involving Africans, Middle Easterners, Latin Americans, Romanians/Gypsies, Polish, Albanians, etc.
I think the belief that Black Americans are the "most hated in the world" gets perpetuated by racist non-Black Americans projecting their own views into the rest of the world or Pro-Black Hoteps who take odd delight in the belief of Black Americans being the most hated worldwide and being "the real Chosen people" and what have you.
But, the more you travel, the more you realize this is false. Black American hatred is very much concentrated in the U.S. itself. Mexican Mestizos in Mexico will treat a Black American far better than he would a Mestizo Honduran or a Venezuelan. Go figure.