You are just inserting the sub-view which doesn't give Jounce the ability to wire anything up because it is handed over to the Xaml parser.
What you would want to do is in the MainPage define a "MainRegion" using a content control. Route the ribbon view to the region and then raise a navigation event for the ribbon view in the Initialize method of the main view model. That will start the chain
you are looking for. You can see examples and blog posts that demonstrate this.