Unity is a very powerful and very complex game engine. Most games only use a small fraction of its features. But no matter how much of it is used, a game which uses the Unity engine must include the whole engine which is a hefty 10MB chunk of additional filesize.

For a very simplistic game like Flappy Bird, using such a huge engine is usually overkill. They can usually be made using just the native Android API which allows to create much more compact applications.

Unity is a very powerful and very complex game engine. Most games only use a small fraction of its features. But no matter how much of it is actually used, a game which uses the Unity engine must include the whole engine which is a hefty 10MB chunk of additional filesize.

For a very simplistic game like Flappy Bird, using such a huge engine is usually overkill. They can usually be made using just the native Android API which allows to create much more compact applications.