Let me help let down the reason why To take advantage of the game engine To take advantage of the easy modding To add in things other players want to see in the game Add in other series such as Halo, Gundam, or something to do with earth and space To enhance the gameplay from best to perfect Look at Battlefield 1942, it was good but people wanted more so they added in more maps, teams, vehicles, weapons and ect to that game that its like having a game collection in one game. edit: Also if there isn't an RTS game of that series people would want to make one so they would mod it into the game such as me who wants to make a Gundam RTS mod