And the number of people outside of a few geeks who care to a first approximation is 0

Closed ecosystem? Sealed environment? Prison? What do you suggest to use instead? The last term would seem apt given the term "jailbreaking"

Personally I do like that. Perhaps we should opt to calling it “proprietary prison”.

I’m in the Apple walled garden and it’s nice. It’s expensive, but it’s nice

Until for any reason you want to leave...

Oh, and what happens then? I’m mostly using Apple devices, but also have a Pixel as a backup phone and a laptop with Linux as a backup laptop. It’s not like I’m locked in the ecosystem entirely.

I like walled garden. Everything appears nice and flowery except for the fact they want to hold you in. You can admire its beauty but can't really trust anything in it due to its darker purpose. Reminds me of the Stepford Wives.

What is that called, an ironic phrase?

I thought that was the point. There ARE flowers and fruits, but only the ones approved by Apple, and the walls stop you from trying anything else.

Hostile external incompatibility?

A walled garden is only seen that way by those inside. To those outside it is a prison camp.