There are so many aspects of fashion, and why it matters, that I think a book could be written on just that subject.
From necessary functionality to playful frivolity to artfelt expression, to lofty self stature and more. Then there are the emotional interactions and effects, as well, not to mention the differences between the obvious....men & women.
I found myself thinking beyond this simple question into realms of imagined "others" and realized that this was a truly thought provoking subject.....with many alternative aspects.