Your page rank is based off the quality of information on your hub, and the overall amount of views it consistently generates. The more you work on a single hub and try to perfect a certain one, obviously the more search engines like google will choose to select your hub based off quality. I would try looking at my Emily Dickinson hub. Its a good example of information in general and usually generates traffic from hub pages and google. Thanks ") If you have any other questions, please feel free to email me.