I got into the habit in the 90's when using it to scroll the page faster. Since I was already clicking on links, my hand was on the mouse. It was a lot easier

I got into the habit in the 90's when using it to scroll the page faster. Since I was already clicking on links, my hand was on the mouse. It was a lot easier to click and drag content than to click the toolbar on the right or to move my hand to the arrow keys.