As the traffic to your hubs go up and down so does your page score. How ever many votes up or down is reflected also in your score. When your page traffic slows down/and or comes to stop it will eventually go into the 50's.
If the pages have been flagged for any reason at all and has not been corrected yet, that too will drop your score or they will unpublish it.
Some of mine have been and a couple are still in the 50's. I deleted some after awhile, and some I improved, added or rearranged. The ones I choose to leave that way is because there's nothing wrong with them, they just get low traffic and/or don't have enough back links to them yet. Not all your pages are in the 50's, just some. :)
God bless you!