Good books. They cover the basic game principles pretty well, which can used in any language and framework. They covered timing and sprites and menus and basic game principles that can be applied in any programming language. Good stuff. And then came the actual development process. I downloaded and installed Android Studio and began to get acquainted with all of its many features. This step tends to take a while, as IDE's nowadays are GB's large and have hundreds of functions built in. Already this step was a bit off putting. Just trying to get a simple 'Hello World' application to run can take hours upon hours.
You might have a really cool idea for a game and have all of your sprites drawn up by professionals and such, but if you're new to a game engine, then it's going to be a while before you can upload that puppy to an app market. Game engines take a big chunk of the work out for you, mainly the tedious work such as collision detection and physics and all of the small intricacies that have to do with images and audio but they do come at a hefty price. That price is the sometimes hefty learning curve.
These games offer the many basic game features such as timers and score systems and full RPG elements and they do so with the most minimal of design. The creators had more time to come with interesting concepts because they weren't busy worrying about configuration issues and app market permissions. They just had a really good concept and they wanted to get it out. Kudos to them.
"...at the cost of more code"
The previous scene isn't too complicated to render. When you click start an interval is created with runs every 20 milliseconds and changes the position of the background sprite. When you hit stop the interval is cleared. Pretty basic stuff and just took minutes to get up and running. If we wanted to however do something a little more complicated, such as let's say have an object detect when it comes into contact with another object which is very common in video games, then we would have a good amount of code to write.