Well, you kind of answered your own question with the word “pressure.” People feel pressure to fit in with others. Since it has become an increasingly prevalent trend to buy new clothing every season, people want to keep up with the Joneses and not be left out.
If you have the money to buy a new wardrobe every season, then kol hakovod (at least in theory; hashkafically there may still be some problems). But if you’re wasting your (or someone else’s) money on clothing that you cannot afford, maybe think about your priorities a little.