It's ok, google has the last word on what apps they allow on their platform. If this app wants, they can build their own mobile operating system, sell billions of phones all over the world, then sell their app on their os. Or they could also try what Epic games tried (and failed). They can build their own alternate play store and host their app on it. Google is not obligated to provide a platform to everyone and anyone.
In legal terms yes, but monopolies should be regulated for a good reason. How about your water supply company cutting you off, because they don't like that poster on your house?
The mobile OS market is a duopoly and only because it's the closes thing to a monopoly they can have without being broken up. Hence Google and Apple can have such high fees which sucks for consumers and app developers, etc.
Within their own platform (the android app market) they are a monopoly.
