[HanyouHottie]

It's easier to understand if you take the motion of a circle to the extreme: Rotate the graph 90 degrees to the right, then any amount up or down, then 90 degrees back to the left. By rotating 90 degrees first, you changed the axis of the second rotation to be the plane normal (perpendicular) to the view axis, i.e. the view axis itself. If you instead drag in smaller circles, then each rotation only contains a small component of rotating that plane so the rotation is slower.