Google offers a push notification system like Apple's, with centralized servers, to efficiently deliver notifications to all users without having apps constantly running in the background killing battery life.

It is unavoidable, I assume, because otherwise you won't get notifications, which defeats the purpose of several apps, and they can't provide a fully independent alternative server because it would require integration on each app developer's backend side. "Sending minimal information", probably means they proxy the requests to avoid giving geoip info to Google about you.