If you open the rear door, you will notice that the bottom of the door is smaller then the part of the door at the window. This is because of the rear wheel well. The glass JUST WONT FIT in this area so 95% of 4 door cars rear glass do not go down all the way. If it was smaller it could, but who wants SMALLER rear windows? Besides, it would not look right with the rear window glass so much smaller then the front door glass.