The value of the walled garden FAR exceeds a single digit hardware sales bump.

the bulk of their sales is, in fact, hardware sales. there is a strong case to be made that such developments wouldn't land people in squarely linux-as-the-only-OS-on-the-device territory either, but rather dual boot ie those users also participate in the walled garden on the mac os side. we've seen this before in the intel mac era.

What do mean by the Mac walled garden?

Using the App Store is optional on the Mac.