A lot of it is down to numbers when it comes to adsense. The average click through rate is 1-2%, so for every 100 page views (from outside of HubPages) you could expect 1 or 2 clicks.
HubPages staff have reported that the average earnings on adsense are $2-$5 per 1000 views, which tallies well with my experience.
A few tips: your hubs are very short. Longer hubs tend to do much better in the search results. I usually go for 800 words + and the majority of my hubs are on page one or two of the search results which equals to quite a lot of traffic (between 4,000 - 6,000 per day).
Adding some images and videos helps to add interest as well.
It's all about producing high quality content. Think about making each hub you create the best page on the web for the particular topic and you will most likely see your traffic and earnings increase substantially.