Don't knock the knock off..?

I'm not a fan of knock offs for many reasons, and I said I wasn't going to talk about them- but! I recently stumbled upon a couple of "stores" on Facebook Market Place and found myself drawn to them for all the wrong reasons. I read the detailed descriptions very carefully and compared all the materials to the real thing, and they matched up! Of course, it's difficult to see what the construction is like from a picture and I did notice some minor differences between some of the fakes and the authentic versions, but overall, I have to say I was impressed. One store guaranteed money back, quality assurance (that made me laugh considering it was a fake lol) and even a certificate of authentication!

The thing I don't understand is why a knock off made from the same materials and undergoing the same process of construction (minus a few minor hiccups in production) cost significantly less than an authentic version? I mean, what the hell are we paying for? A slight difference in the tension of the thread used in the stitching? The absence of a couple misaligned stitches that no one, without a purpose and a magnifying glass, would ever notice? I guess what I'm wondering is, does a good knock off stand the same test of time that an authentic bag would? And if not, what is the "shelf life" of a fake vs. the real deal? And is it still worth the cost difference of thousands of dollars? 

Hmmm..., I guess it'll always be a mystery to my middle class mind. My father once said, if you can't tell the difference between chicken and duck- order the chicken. lol.