Because greedy HubPages don’t want your links to be "dofollow", that is why. Your hubscore will keep falling if you're inactive.
Most people here don't even realize why HubPages was created in the first place, It’s about article marketing. But because of Google Panda and some other changes, HubPages and many other article directories went “nofollow”. If your hubscore is below 75, all your links become “nofollow”. http://en.wikipedia.org/wiki/Nofollow