Why is there still racism in the world?

I just don't understand it. So i tried dating a country white guy (who was not all that intelligent so it didn't work out) and some of his family had a problem with him dating a black person. I'm mostly Puerto Rican and then i have a little bit of black and..well a little bit of everything in me to say the least. I don't understand it at all! Why do people still care about race in a relationship??