Because develepers told me, also here is the comparison with a real one it was based on: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-3A4OWlzkrro.html
They won't add tanks because it would change the ESRB rating of the game and they won't add tracked vehicles, because they don't really know how to make them work with game's physics engine (at least for now)