If that still sounds like recursive nonsense, think of it like an inside joke. Let's say I'm a fan of the show Rick And Morty, and I hear somebody in the break room at work pause from making their sandwich to say, "I'm a pickle, Morty!" That's not a statement or even a joke -- it's intended only to communicate that they are the type of person who loves that show. If I respond, "I'm Pickle Riiiiick!" then there is, again, zero information in the actual words. To an unfamiliar listener, it's nonsense. The only thing my response is communicating is "I also speak your language," because my ability to speak that language means something important.
Well, most fashion choices -- the careful selection of brands, the fierce rejection of looks that are outdated or out of season -- are simply communicating "I know what the secret fashion rules are, and am able to adhere to them." This, incidentally, should clear up a common source of confusion among guys who'll see a girl dressed in "provocative" clothing and say "See? She wants men to get aroused by her body!" If you ask that woman, she'll say she dresses to get compliments from other women. She's not lying.
It's kind of like how guys buy sports cars even though they have no intention of ever going 100 MPH down a winding road, or how gun enthusiasts buy assault rifles even though they don't anticipate a firefight. We all buy things that are "sexy" for reasons that are often far removed from sex. Instead ...
It's About Status (Not To Be Confused With Wealth)
Let's all admit something: Every single person reading this treats people differently based on how they're dressed. If you get a knock on your door in the middle of the night from a stranger asking for help, how wide you open the door will depend largely on what said stranger is wearing. A well-groomed man in a suit will get a different reaction than that same man with a week's worth of stubble wearing the top half of a clown costume and absolutely nothing else.
What we forget is that we are always in the position of the plaintive person on the other side of the door, 24 hours a day, only being evaluated on much finer criteria. You are continually being judged based on your clothes, shoes, jewelry, hair, hygiene, posture, and mannerisms by people who are trying to determine one thing: your social status. Not how rich you are -- that's but one factor (the law student may have less money than the local meth dealer, but clearly has higher social status).
For uncool people like myself, what hits us like a truck in high school is the realization that humans (and all social animals) develop hierarchies which determine who has access to the best food, mates, etc. Ideally, that status would be based on who is the most fit -- which ape is the best at fighting, mating, socializing, and ... who can fling their shit the farthest, I guess. But your abilities are worthless if you can't convey them to other members of the tribe. That's why we need things like clothes and cars to signal our status.
The reason the fashion world seems so frivolous and petty is that at some point, style only serves its own purpose. In a sufficiently complex society, the most important ability isn't fighting, socializing, or mating, but conveying status. Now hang on, because we're about to go down the rabbit hole, here.