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?
No. The GPL for Linux applies to the Linux kernel.
GPL only says that one particular program has to stay open. It doesn’t say that everything else on the same computer has to be GPL.
Most Linux distros include software with a wide variety of licensed. Many people run commercial software on top of Linux.