Apple built, run, maintains and owns a stadium. The stadium has a food court with many food stalls.
Some of them, Apple runs themselves, but tons of others are run by people who pay N% of their revenues to Apple to be able to have them.
They still need to supply their own food, branding, marketing, furniture, and pay their staff, Apple gives them access to the stadium crowds and a payment processing system.
Apple is not obligated to advertise those third party stalls over their own.
If they don't like the arrangement they can always go somewhere else (there is an even bigger stadium in town that has available food stalls).