Why do people still continue racism?

Racism is likely triggered by social upbringing, experiences, and perhaps partly instinctual.

Social upbringing is usually the most popular amongst racists they are normally taught racism at a young age.

Some people who were not previously racist have bad experiences with a certain race and become racist afterward. Rape victims who were raped by a person of another race may become fearful, resenting, or sometimes even hostile to the race the rapist belonged to. So traumatic experiences especially can cause racism.

Then there are explanations of a instinctual level. Because a person of another race is genetically different enough to be a visible difference it can cause conflict as both parties wish to pass on their genetics and may see each other as a threat to such. However this is not necessary as all races are currently still genetically close enough to create healthy children together. However if given enough time and if races did not mix we would continue to grow separately apart from each other to the point of not being genetically compatible. Our ancestors and the neanderthals went through this.