Most of our apps are specific for certain tasks requested by client, and this will not make so much income!
People especially recent generations; need exciting social apps ..
Case study: Our National Intelligent "spy" system made an app under fake producer, this app is exciting for almost of our country people, the app when installed it takes all contacts details & save it in app server side database, then all people who installed can search in other people contacts!!!! Almost of people are happy here!! I'm shocked why Google approve it on its play! It has almost of dangerous permissions! The app has ads, every single search is parallel with ads.
This is app is reverse social engineering, spy-er behind it can get alot of social information. People who install it comment on app store wall that app is spying on them, but they are happy with it!
In this case we can see programmer can gain good passive income as b4xer said, but we as programmers kept us in a very narrow zone! we should fight & create exciting IDEAS.