If There Are So Many Advantages to Selling National Brands,why

If there are so many advantages to selling national brands,why do retailers even carry private brands?

A) Private labels yield higher margins to retailers.
B) Private labels require less investment from a retailer from design to display.
C) Customers have loyalty to national brands.
D) National brands are better quality overall than private brands.
E) National brands offer a retailer more flexibility on how merchandise is displayed and advertised.