Almost two decades of Google market dominance with Android, and Google's simultaneous ownership of the entire ecosystem, including the browser, search engine, cloud integration and the internal app store (which is integrated so far up the OS's ass you can't do much without it). You just can't enforce a monopoly like Google does and simply claim "why wouldn't the competitors and consumers just kneecap themselves to leave??"

You'd have to get every single app developer to implement an Amazon variant of Google Play Services alongside Google's.

That's not going to happen, it's already a large problem in China.

Play Services, and the Play Store. The network effect is so strong that competition becomes impossible. Nobody would buy a phone with a different AI provider because you couldn't use apps like Uber, and Uber wouldn't develop and publish to a different store and re-write their app to avoid Play Services to target a platform without any users.

You’re not being clever like you think you are. “They could simply build something else” is … something that truly everybody knows. That’s not the point.

Why didn't Linux programmers just fork Windows or iOS?

What's stopping you? Reflect on that and you'll have your answer.