[jonpurdy]

You're likely correct: it feels like it wasn't subjected to any UX research. Knowing how Apple works, it was probably demoed in front of a few higher-ups, but nobody other than the person or team writing it used the feature long enough to notice that some people would be confused by it.

And you're correct, I never use full screen. I don't think it's weird to use it, it just doesn't suit my workflow (single large monitor, so I need a lot of stuff side-by-side).