I thought the same as you until I once got a new Mac and forgot to switch off natural scrolling during the initial setup. You scroll down on a page far more of

I thought the same as you until I once got a new Mac and forgot to switch off natural scrolling during the initial setup. You scroll down on a page far more often than you scroll up, at least in my day-to-day. Natural scrolling on the mouse wheel makes scrolling down an easier motion on my right middle finger than with classic scrolling. It's easier to push out than to pull in.