Retailers don't want to expend money and other resources on security personnel and equipment. Unfortunately, they have to do so because certain individuals do partake in behavior that harms the store in one way or another.
If a given store repeatedly has trouble (or a lack of trouble) with individuals who have certain traits in common, perhaps even including skin color, then it's understandable that people exhibiting such traits may be treated with a certain degree of suspicion.
The store is merely trying to manage risk in an efficient manner, rather than intentionally giving people with one trait an advantage over others without that trait.