Why is adding a drive a supplementary action, but flipping a drive to a higher number an anytime action? Shouldn't they be the same?
They once were. But it turned out to be more fun this way.
Getting the drives takes you an action (or some bonuses). Later in the game you can spare this supplementary action. It would not be fun to still have to do this kind of "supporting action" over and over again. Because you can use the portals better the way it is now...