I can access the whole catalog in Catalog view, the functionality that you are looking for is full catalog view in favorites. It appears that Favorites are now focused on providing an access point to adding favorites to new projects, which is quite different.
Catalog view is quite powerful in what it can access, and you can even add folders to an existing project even if they are in favorites... and explore your folder that is in Favorites there if you forget.
I suppose regression in the UI is one way to look at it, but esri didn't set out to make a clone of ArcMap 10.5... that is what 10.6 is.