Fun fact, I spent more money on GNU/Linux and donations to FOSS projects then I ever have for Windows and its software. Why because it is just better more user respecting and is constantly improving, and the opposite is true for Microsoft and their malicious business practices and bad products that are getting worse by each release.

Google made money on Android. As long as you're not making direct changes to Kernel code, you're free to close source anything you add. The existence of AOSP didn't prevent the Playstore or google play service from making Google the sole controller of Android. That's how it turns into a goldmine.

Android is kind of pointless without phones it is running on, so having a code does not mean you have any use for it. Same for routers using Linux. Kind of pointless to have source code when you don't have the hardware.