What I'm referring to as a walled garden issue is that they've learned to use the "included" features like iCloud etc, those are walled in (ie using it on Android isn't as smooth). Thus when you switch away, you're expecting them to learn the new UI and to get used to different services (eg google drive) and their associated menus.

I suppose it's better described as vendor lock-in, similar to how before you could easily transfer your phone number between carriers, the number itself acted as a form of lock-in, if you used the number on anything important you were stuck with the number until you could get the number updated.