I think the reason Apple also went with natural scrolling for mice is because of their Magic Mouse which attempts to act like it’s a trackpad. The gestures are similar to how they are on their trackpads, so it’s consistent.
Touchscreens and trackpads? Natural scrolling all the way, we’re directly moving the content. It works the same as if your two fingers were click and dragging the content, it does feel pretty natural.
With a traditional mouse, I see the wheel as already inverting the movement: imagine the content is the mousepad, traditional mouse wheel direction scrolling down would be pushing the content under the mouse upward. Although I think the real reasoning is probably just either you’re controlling the scroll bar or the engineers just thought that’s what felt natural and intuitive to them at the time. It was probably born as basically just a more granular page up/down button that became a wheel.