When you look at the table of which big digital marketplaces sell what kind of experiences - books, movies, TV, apps, music, games - it certainly looks like there's lots of competition, and there is. However, the lack of compatibility and the abundance of DRM in the space makes each choice much more "sticky". If you buy a Microsoft Surface, for instance, you won't be running any Android apps. If you buy an iPhone, you will find yourself also buying your music, your books and your movies from Apple, too, because they won't work anywhere else. And the more you buy there, the less you will be willing to change platforms. You make your choice once, and then the inability to pick up your stuff and take it somewhere else means that you are stuck, unless you are willing to abandon your whole library and start over.
Furthermore, even where there is some compatibility (as with, say, the Kindle app on Android) you are unlikely to take advantage of it, because the fragmentation of your library is a major pain. I don't want half my books in the Google Play Books app and half in Kindle. Why would I? I'd have to remember what collection each one is in, and that's more likely to depend on purchase price than on any kind of theme. It's far easier to choose one platform and stick with it, because anything you buy in one place is locked to that place. You don't own it, you just pay to look at it through a window. If you walk away from that window, your stuff stays there, because it was never yours. Human nature fights very strongly against that kind of sunk cost. If I paid for it, then I feel that it is mine, and I shouldn't be punished for wanting to take it elsewhere. Because I am prevented from taking it elsewhere, I stay where I am and defend the one choice I made several years ago.
This is the way we are building the world now: all the world's media is sectioned into a series of deep holes, and you get to choose which one to jump down, but only once.
Mokalus of Borg
PS - I'm not a big fan of deliberate incompatibility.
PPS - The best software needs to be compatible with multiple other programs or else it's pointless.