The results you see here is obtained from about 6 apps. Building an app takes about 3-4 hrs of work. So, you can build an app per day. Yes, there are apps which donot bring any clickbank sales. Also, not all of your apps will bring sales. So, you can monetize them with adsense.
So, if you focus on this, you will start seeing traffic. And with increase in traffic the chance of making sales increases.
Now, it's not like any paid traffic methods where you spend more money with more number of campaigns.
You can build and publish as many apps you want and google app store will not ask you for money for each app. You just have to pay one time activation fee of $25. So, you are getting unlimited traffic for just $25. Isn't that amazing! Now, why should one even look at other paid traffic sources when one have google app store account. One can get lots of traffic and convert that to money.