I imagine there are a few potential causes:
1. Light content. You can fix this by combining the pages for terms together, and using anchor tags to point the user down where they want to go. On your front page include more of the post - right now it seems like the intro blurb is only several words long.
2. Duplicated widely. You mentioned this in another question, and I'm not sure what else to do here. You're already using rel canonical which would be my advice.
3. Tons of links on every page. Your footer has a ton of links, and the menu is quite large to begin with. Consider removing most or all of those footer links.
Best of luck!