Why Android device screen rotate only in Portrait and Landscape orientation? I have android device LG E400 which has only two types of orientation first one is Portrait and Second is Landscape.
It works on 90° Orientation(Left Landscape), 270° Orientation (Right landscape). Why can't it rotate in 180° (Bottom side to Top ).
Why Android OS couldn't have made that feature yet?
Some phones do not support 180° rotation because it is not supported by the rom. A lot of manufacturers prevent 180° rotation I believe for sake of simplicity. Theoretically, you only need one landscape mode and one portrait mode for basic functionality.

To fix this 'problem' you could install a custom rom that supports 180° rotation. Alternatively, you could root your phone, install the Xposed framework, and install a module that will enable all rotations. I have also heard that there are apps that let you do this but I have not used any myself and therefore cannot confirm if they work or not.