Because while both the server and the client are Open Source, the server doesn't federate. If you want to be able to communicate with anyone, you have to use th

Because while both the server and the client are Open Source, the server doesn't federate. If you want to be able to communicate with anyone, you have to use the official server instance. And the official server instance doesn't allow unofficial clients (though some clients seem to get away with it for a while).