Indirectly, the issue is rather that they will ban you if you don't use their client, even if it comes at no cost to them (setting aside losing the ability to run spyware on your device). It doesn't need to be a tty client, it could be a client for a older phone, a native client for GNOME, a client with more features and extensibility, or whatever. They do not know best what every person's wants or needs are. And until this issue is overcome (which I don't expect it to be), the service is unfit for general usage.