Why are some Arabs and North Africans so racist?

I’ve been a muslim since birth and i’ve never had an issue with my religion until this year. I’ve done more research and I’ve started to become more aware about how deeply racist the Arab/Muslim community is. Starting from them creating the African slave trade which is still going on in Lebanon, Kuwait, Saudi Arabia. The mosques I attend are predominantly Arab and they’ll always end up excluding black patrons and avoiding standing next to them during prayer. Some even didn’t want to salaam back to them. I took a trip to Saudi Arabia this year and I was called “Abeed” several times by some young boys(found out what it meant later on) and was asked if I was a maid/servant by several different women. I don’t understand how a religion based on inclusion and the idea of everyone being equal could permit slavery and have such extreme racial biases. I’m just wondering if black africans did anything to arabs to make them have such an extreme distaste towards them? I know some people will reply with the defense that black africans are also “racist”, but I’ve never seen anything on par with slavery and we don’t have any special word used to insult Arabs from what I know.