Due to the simple reason of there not being a single game on the Xbox One or PS4 that uses the keyboard and mouse system. Also, it is not know if the Xbox One and PS4 versions of the game include the command console.
considering the consoles have on-screen keyboards and (currently 3rd party for ps4 anyway) mini keyboards that clip onto the controller, it shouldn't be much of a problem to implement.
This should be present. It already is with the PC Version with a controller. You can select things in console no problem then type them out on the keyboard. The feature for the console should be keyboard exclusive really, theres no real need to add in another secondary as you shouldn't be doing it without one.
It might not be Beth's choice.
I remember reading a long time ago that the companies, Microsoft/Sony, wouldn't allow games that allowed keyboard imput. Use the keyboard for messages/chatting, yes. Use the keyboard for game control, no. If that hasn't changed, Bethesda wont be allowed to add a command console for consoles to the game.