Nowadays, Google seems to be stricter in accepting people to AdSense. Before, it used to be that people easily got accepted even with only a few hubs but now many are being disapproved for insufficient content. I also got disapproved for the same reason when I applied and only had 11 published hubs at that time.
Many are saying that you actually need at least 25 or so hubs so you won't be rejected for insufficient content. That's why I plan to write more hubs before reapplying again. If you go to the HubPages forums, you'll see many have been rejected by AdSense for insufficient content and those that have finally been accepted had written a lot of hubs before they got accepted.
Just remember to write hubs with high quality and content. It might also help if you try to follow the "need some goals?" at the top of any hub you're working on in edit mode. You'll need long hubs with images and even things like polls or videos. Having evergreen content helps too.
Also, make sure that you read up on all of Google's terms of service, policies, guidelines, rules, etc so you're not inadvertently violating any of these. Just be sure to follow all of Google's terms and criteria. Hope this helped and that everyone who still hasn't been accepted into AdSense can finally be accepted.