Why the file size is so big?

Hi, I recently made a demo game project. the game is like 2D casino game. For this demo, I didn’t used a single image not a single sound file. All I used widget blueprints and lines of blueprint codes.
After I finished the game the file was about 12 MB in size but when I made an Android APK the apk size was 169 MB!!!How? I don’t know why the file size is so big.
I followed some instruction about shrinking file size in my other projects but it just reduce 1/2 MB of total size.
I really need help for this, if anyone have any Idea how can i reduce the file size please help me.