multicolorguru hit the nail in the head.
More traffic and more importantly better targeted ads with SEOed content.
One of the niches I work had a similar problem, once I did some good
seo on the page, my click through rate tripled.
It was around 5% which is average for my niche. Then I got it to %15, sometimes 25%.
Also think about what traffic pays.
For my niche advertisers are only interested in USA, Canada, UK and sometimes AU.
When I see too much low quality traffic from other countries I block or redirect them.
It brings up my click through rate and it raises the $ of my average click.