If Britain and America are racist societies, why do so many Africans and Asians claim asylum there?

It has often been claimed that Britain and America are racist societies, where black people are held back by endemic racial prejudice which prevents them from fulfilling their potential. It is curious to observe though that refugees and asylum seekers from Africa and Asia seldom head for supposedly more progressive and forward-thinking countries such as China, Cuba and Vietnam. Their chosen destinations are invariably two of the most institutionally racist countries in the world.