I don’t understand why Google didn’t just made Android closed source. They would’ve made custom roms impossible and therefore more able to control and spy on it’s users. Why did Google made Android open source, while Microsoft’s Windows is still closed source to this day?
You can’t take an open source project closed source, not easily. They are usually published under a license that makes sure they stay open source.
Google didn’t create android, they bought out its creator. That didn’t mean they got to own the code. Plus it’s built on top of, and still runs, the linux kernel, which is also open source.
It’s the same for chrome, chromium is open source to this day, but that’s also one of the reasons why it’s so wide-spread. Anyone can use the code, so they do. But google didn’t make it, it existed before their involvement.