DeGenerals are currently focused on adding various features to the game so implementing new vehicles isn't a priority. Even when the time comes for them to work on adding new vehicles, it isn't just a case of spinning a wheel and adding whatever it lands on, they need to find which vehicle they want to add, see how many sources are available and if there are enough to use that are legitimate and accurate, and then need to be able to see if they're capable of replicating it, and many more processes.