> It's rather sad that Google needs to pay Android makers a fee for installing it's apps, given how Google gives away source code that makes Android exist in the first place.

This is a very innocent view of Google's business practices in this area. Google has a tight hold over most device makers through anti-fragmentation agreements and other contracts if they want GMS and want early access to the non-public AOSP tree, which is a practical necessity to ship cutting-edge Android devices. Aside from hard legal power, Google also projects soft power through their control of the ecosystem and device makers wanting to maintain good relations. As a result, Android-derived innovation in the ecosystem is highly constrained even if AOSP is open source licensed since device makers and manufacturers cannot ship devices with Android-derived operating systems in device categories enumerated by the AFAs unless the devices pass CTS (which prevents most kinds of serious divergence from Android).