Why is Enlightenment so difficult when you have to do literally nothing?

Meditation is not "nothing". Self control of our minds and thoughts is far from easy and requires strenuous effort until the mind has been retrained. Try it and you'll see. It is not unlike training your muscles to do certain things well, such as throwing a ball. It requires practice. So does training the mind. In any event, it is not so much a philosophical problem as it is a psychological and physiological one.