Why does the external mesh pocket have a...
Why does the external mesh pocket have a waterproof zipper?
Good question, I'd ask TNF design team if you want a straight answer. But yeah, it's pretty unnecessary.
If any stitch is not waterproof, then the bag itself will not be 'waterproof' as water will be able to enter the bag. Though the zipper is for an outside pocket, it is still stitched to the bag itself creating a possible entryway for water. Hope that helps.