I still think you're looking at competition slightly wrong.
Coke and Pepsi do compete with eachother, along with the rest of the drink market. And overall prices in that industry are pretty low, some people will buy other competitors (the store brand Cola's). But overall competition is working.
Apple only kinda competes. Sure a phone is a phone and a laptop is a laptop. But unless someone is entering the market for the first time. They already have applications they are looking to use, so if you need an iPhone, you need an iPhone, and same for a Mac. But if you're an android or Windows user, suddenly you have a lot more choice because there is lots of competition!
The reason companies setup walled gardens, or pay for exclusive access to a piece of media is to erode competition. If a user wants that thing, they can only get it from that one place.