Microsoft Store apps missing from new Intune store app deployment?

We're looking at moving our current Store for Business applications over to the Microsoft Store App (new) app type - but a few apps we use appear to not be available to add in this way, for example, iTunes, Client Center for Configuration Manager.

It does say in the documentation that some apps may be unavailable for deployment due to region, age, or other restrictions, but I can't see any reason that these aren't there. Anyone have any ideas?