Double Work for Replacing This Jean Zipper

I have never seen a zipper constructed like This. It honestly wasn't too much different than replacing a regular jean zipper. But sometimes ya just gotta ask "Why?"

	At first I was confused by this extra fabric. What is going on here? Of course I had to take my own instruction, here. I begin almost every tutorial with Step One: Examine the Garment.
	After a closer look, I determined which stitches to rip out and where to place the zipper. Everything had to be attached to the inside fly area.
	Lastly, I had to attach the fly to the outer pant area and topstitch. Do you know why they made this like it is? Leave me a comment if you have it figured out!