Notifications in mobile apps aren’t easy. A developer can’t just write code for the app to poll the server every x minutes. When the app isn’t at the foreground, it’s usually frozen and can’t execute any code. So, to get notifications, the app must rely on the host operating system and must have a server running somewhere to talk to the OS. Servers cost money, so now the developer must charge something from users, or sell their data, etc.
So, rejoice on the fact that Voyager is putting you in control of your data, ethically. And just check the app every now and then.