What they really want is to be the iOS and the App Store. They don't want to live under Apple and Google's roofs anymore. They want control. And they want to be the one taxing apps 30% instead of Apple and Google.
Maybe, they do have their own store for VR apps but they also allow you to connect the headset to a gaming PC and use Steam games. They also support OpenXR. So they don't seem to be building a walled garden, more like a garden with a fence you can step over. Maybe that'll change in the future but if it does they'll piss off a lot of their customers and force them to switch to other hardware.