It makes sense on a trackpad too which is what the majority of sold Macs come with. You’re “pushing” the document, not moving the scroll bars. Seems perfectly natural to me. My fingers move up, the document moves up; just like what would happen to a piece of paper being slid up a table.

Yes, it’s less direct than touching the screen, but it makes more sense for the model of UI they’ve been going for over the last 20 years where the content of the window is more meaningful than the window itself, which is to say worrying about where the scroll bars are rather than what part of the document you’re looking at is what’s not natural.