I came to write exactly this. The app ecosystem grew due to the insane numbers of users having a >50$ smartphone everywhere in the world; and this is what made fb and the rest of companies what they are at the moment. The price barrier to enter the vr/ar world would be considerably higher and almost unreachable in the 3rd or developing world, which is fb’s main audience.
There are so many apps targeting people in developing countries; fintech, crypto, ads, commerce, etc all accessible by a 50$ smartphone from some remote city in Nigeria or Guatemala. I can’t really see a vr/ar marketplace targeting these people, but perhaps i am short sighted.
