I guarantee you somewhere in their backlog is an item that says "require app store for app installations on macOS"

Apple isn't the company that has already attempted to lock their PC operating system to only accept apps from an app store.

That's Microsoft with both WindowsRT and Windows S.

Just because the first attempt failed in the marketplace and Microsoft backed down on the second doesn't mean they haven't already tried to lock Windows to only run app store apps multiple times.