You are missing a major issue here: spam. E-mail and phone calls are riddled with spam precisely because these are at least somewhat open systems.
E-mail is unusable without running it through a ton of spam filters or (more commonly) letting someone else with a larger data set do that for you.
Phone calls are in some ways even worse. I no longer answer unidentified calls, period, and I keep my phone on vibrate at all times. Any important calls must be scheduled. I get 2-4 robocalls per day. I'm tempted to change my number but I've heard it doesn't matter.
Spam is a huge reason walled gardens win. Anything open gets abused to death.
Another example is closed OSes like iOS. Consumers love iOS because you almost never see malware. Open OSes easily acquire malware if the user is not tech-savvy (and even sometimes if they are), and finding software outside a walled garden is an exercise in picking your way through a minefield. Have you tried to search for a Windows app on the open web recently?
