Why did shakespeare make Richard III look bad?

Shakespeare did not create the story about King Richard III and his actions; he got much of his information from an unreliable historian of that time. King Richard was killed before this historian even began, so all records and tales were secondhand from others who would tell tales based on their perspective and bias for a variety of personal/social/financial/personal goals and desires. Even after his life, Richard III suffered from poor public portrayal during this era.