If you go to a grocery store, you'll find many versions of cheddar cheese specifically. Some of it is blocked, some slices, some shredded. You'll also find that in at least one of these forms, the store has it's own brand – called a "private label" – of cheddar cheese, probably shredded. Because Kroger, or Wal Mart, or Whole Foods has said "hey, selling cheddar cheese is a good idea and we can compete in our own stores". So they make a competing congruent product, maybe quality and prices are lower, but that's OK. The customer can make their own decision on which cheese to buy.

This is exactly the same concept as Amazon's private label businesses.