This has been suggested, and answered many times. The response is that is will be added to steam greenlight once atWar is more polished up, and there is more mobile capability (this is what I have heard, and I'm sure others have heard same response, maybe worded differently).
I agree, I think this game would do great on steam, but only after certain things are altered/fixed. I don't know if atWar servers could handle all the players that would try the game.