Anyone thinking about going into app designing to make money may want to think again. About 99% of developers don’t make money.
About 1% of app developers manage to make decent money from their apps. Bear in mind that many apps on the app store are copies of other games. Candy Crush has been successful for its developer but then copies and similar games began appearing on the app store in the hope of cashing in.
If you want to make money on apps then you are going to have to come up with a game that is exciting and different to the others already out there. Flappy Birds was an example and this made the developer a lot of money.
Google likes to brag about the many apps that they have but then many of these are copies of other games. To them its quantity over quality it seems.
If you want to be in the 1% that does make money then you need to design an app that is new and which keeps people coming back for more.