The difference is that retail is split over many companies and there is good competition. You also have the option to open your own store to sell your products.

The difference is that retail is split over many companies and there is good competition. You also have the option to open your own store to sell your products. You don't realistically have that option for phones. It's insane to require a company to build their own phone hardware, OS, app store, and get the majority of people to switch over to it before you can sell books without paying a 3rd party for it.