I think what happened here is that one of the major sources of app discovery now are the "Apps Gone Free" apps. It was precisely because it used to be a paid app that suddenly was free that suddenly put it in front of so many people.
Now, if the app is truly worth recommending then it could become paid again and word of mouth will generate sales.
Again, this is all completely obvious but there's still some magical thinking when it comes to the app store that somehow normal rules of selling a product don't apply.