Earlier quoted context omitted.
The restricted App Store does add customer value, and that customer value is degraded if there are other App Stores available. Namely - if a user buys Apple products because they want the security/curation/whatever that comes with Apple's walled garden, that advantage is broken by forcing Apple to have other app stores on their platform because now that user cannot get all the content through their trusted source as…
So having more than one app store degrades the experience of people who choose to use Apple's app store like having more than one newspaper degrades the experience of people who read the New York Post.
The choice of app store isn't ever in the consumer's hands, its in the corporations hands (Apple or otherwise).