This is a very HN view of Android. The "openness" of Android was for mobile device manufacturers, not app developers and end-users. Android's prominence was driven by the myriad of low-cost Android devices by multiple device manufacturers, whereas iOS is only available via iPhones.

The vast majority of users don't care about "openness" of the OS. They care about the utility of their phone in everyday life.

Can I access digital payment systems, social media apps, and entertainment apps? How's the camera on the phone? How big is the screen? Is it waterproof? How expensive is it?

These are the questions the majority of phone buyers care about. Not, can I download an app off of a random website and install it?

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I would say that the majority of developers don't care about the "openness" either. They care about accessing a wide audience and getting revenue from their work. Free apps without ads or in-app purchases (zero-revenue apps) are the minority.

Google is also fine with losing the zero-revenue app developers because they provide no value for Google. Actually, they are probably a loss for Google, since Google provides Google Play Services.