Not all the brands Costco features are the same quality of the non-Costco brands.
They get to keep the branding, but they give the specs to the manufacturer of where to cut costs.
The finer details get deleted which make up why designer denim is nicer than regular stuff:
https://www.facebook.com/Costco/posts/10151748687449947
This kind of thing is really evident in Ralph Lauren's Polo line up. You can find "Polo's" for $9.99, but the material and stitching/etc are no where near the quality of a $60+ three button.
Do they look nice? yes. They just don't wash and wear like the more expensive ones. The cheapies lose their shape and get all pilly/fuzzy too quick.