Very simple: Google doesn’t sell Android. They sell mobile devices that run their version of Android. The profitability of their mobile business overall is unclear (we’ve only seen numbers for specific phones). Can you cite your billions in profit claim?
You're separating the fact that Android is OSS from the fact that google running Android allows them to run the Play Store which made billions last year. It also lets them have Google Search be the default on all those devices. Google themselves account Android this way, attributing some amount of the profit from those things to the fact that they run Android
