There are plenty of free games on the App Store and Play Store. There are usually one or two catches with them though - they have ads to provide revenue, or they use in-app purchases to unlock extra content (or to simply remove the ads). I wanted to make something simple that was completely free, no strings attached. No ads. No IAPs.
I've been working on my own 2D Android game engine and most of my projects have been experiments revolving around it. One of the experiments was connecting to the Google Play Services to implement achievements and leaderboards. I decided to be clever about it and integrate it into the engine itself, to save the hassle of implementing it on a game by game basis later down the line. That turned out to be a bit of a mistake.