because big SUV,s have the big window,,and the way the vehicle is built,,it catches a lot of dust and dirt,,and needs to be cleaned off,,most cars have a trunk area,,and this helps prevent things from getting slung up on it,,there are some sedans that have them,some Honda cars have them,,but they are needed on a SUV,,other wise you,d be out there cleaning he back glass all the time,,ad this would be no fun in the rain,,i hope help,s,good ,luck.