Most of those pockets, notice, are in the side seam itself -- allowing them to be made without changing the order of construction, but requiring a zipper to keep things from falling out.

I realize that within-the-seam vs, welt pocket is externally a small thing, but it changes the order of construction dramatically. My approach doesn't need a zipper to prevent things falling out, but does need a reordering of the construction process, and so is much rarer to see for exactly the reasons I enumerate in the post, even in spite of being potentially materially cheaper.