So, have you tried putting your apps on Google Play (or SlideMe, Amazon) and then simply waiting for downloads from search/front page traffic, without any attempt to promote the app (no facebook sharing, no paid ads etc.)?
In other words: do you get good downloads of your apps from “organic traffic”?
Of course not. If you have not did the work of app promotion, your app will be disappeared very soon, and you will not get much revenue in return. Therefore, in order to get more installs, you have to try your best to optimize your app. If you have enough budget but limited time and effort, you can collaborate with a reliable app store optimization company to help you.