Have you seen a Ferrari engine inside a Smart (car)?

No?! Now, guess why!
You can use the same logic for Unity engine and Android. (Ren'py use a different engine, which makes them easier to port to Android.)
I'm not saying it is impossible - because it is possible -, but to port a (unity) game to Android needs to be compiled different as to Linux or Mac.
Most mobile devices use a ARM-achitecture (CPU) and a PC/Laptop a x86-architecture (both CPU-architectures provide 32bit and 64bit support).
A port to Android at an early development stage like Timestamps is right now, is a waste of resources (time and money), so maybe after the game is finished and there is a profit in the mobile devices market, maybe then a an Android version will be available.
I really hope before we see an Android version, we will get a native Mac and Linux version of the game!

*dream*