...because there are 15 hubs, all on different topics. Not to sound harsh, but that's barely getting going, and not really enough for people to find you organically very easily. I'd also wonder if you have paid attention to keywords, as well as the commercial viability of your hubs. We're paid by sales and advertisements, so it depends very much on the number of sales and how much advertisers are paying for ads on that topic.
From what I can see, you have an awesome start. In the world of open-submission, however, it is still just a start.