There are many reasons. First, the conflict between the leaders and the people. I think this conflict result to the fall of many dynasties in Chinese history. Thus only you love your people, your people will love you and your rule will be longer.
Second, zhouyouwang put all his thoughts on the beauty and never care about the politics and the economy of the country. This might be the direct reason for its fall. Of course the reasons are not just the two, but i only know this. Hope it helps!