The short answer is that ARC is version 1.0, other features will be added overtime.
Why? So Roon could get ARC out to its users now rather than keeping people waiting.
Check out Feature Suggestions there are quite a few topics there now about ARC.
https://community.roonlabs.com/search?q=ARC%20%23feedback%3Afeature-suggestions
Including this one
Check them out and add your votes accordingly.