Because people do not look beyond what they see.
Face it. There is a correlation between race and crime, as well as race and poverty, both local and global. So people see this and jump to the conclusion that coloured people are inferior
But we know this is not the case and its all to do with other socio-economic factors. Education is the key to stopping racism. But first we must acknowledge that the 'black' race is not equal to the 'white' race, as a group its poorer, less education and has more problems with crime. If we just cover our ears and go 'blah blah its all good, stupid racists are stupid' we don't solve the problem, we further alienate those with racist views. The problem needs to be confronted head on and we need to say 'yes, these are the problems, but this is why, its nothing to do with the colour of your skin'.