How do I install an OEM's launcher in my device?
The apps made by OEM are specific to their devices and ROMs.

The apps may depend upon external libraries that the phones don't have..


  Anyone having a device made by those OEMs should be able to upload the APK of their launcher, so why it is not possible to install them? As an example, see How to download and install Samsung TouchWiz launcher any Android device?


You can directly install the APK, but it won't work.
Because, you need to place the lib files in the /system partition necessary for that app.
That's what flashing the zip file does :)

The only way to get it working on other devices is porting the app by editing and linking the necessary library files.