If I understand you correctly, you are writing hubs that don't seem to have any advertisers?
The volume of ads in the Google network is driven by the number of companies trying to sell products or services. Advertisers go where their customers are located. If a niche is too small (not enough searchers online), that niche may not have any advertisers.
If you want to make money writing on HubPages, your best bet is to write about popular topics (lots of searchers) with some (but not an overwhelming) number of advertisers. Your should start with good solid keyword research to pick the topics of your hub. Search the hub community and you'll find great tips for doing keyword research effectively.