Why? Because we all have things we think are cool. And we do want to signal what we think is cool.
For Anna (if I may be so bold), "cool" is "I follow fashion super closely because I think it's an art form, and I choose to signal my knowledge of and appreciation of that art form by wearing high-end, cutting-edge designer items."
For Una, it's something like "I think it's cool to be a little quirky but I also appreciate great workmanship and great materials and oh by the way my heritage is Indian and I'm strangely fascinated by the whole British Colonial thing for some reason."
For me, it's "I follow fashion closely enough to know that Burberry is a 'thing,' but I am far too cool to actually splash out the money required to have a real Burberry scarf, because I am an intrepid world traveler and I would rather splash out my money on a luxury river cruise to a developing country where not many Americans have yet been as tourists." AKA "Oh, this old thing? It's fake -- I got it on a Cambodian riverbank!"
I don't see anything wrong with any of it, as long as we are all respectful of the fact that coolness (and snobbiness) are in the eye of the beholder and generally we all have our quirks and Achilles heels and blind spots, and the thing that makes this fun is that we're all different but we all love fashion!
/rant