The purpose of this shirt is for the person who bought the shirt (and that person alone). It’s a reminder that when you put on your t-shirt, you know the price. You know how much money you have that you can afford to drop $120 on a novelty. This confidence will undoubtedly make the person wearing the t-shirt, wear it better.
Additionally, this solves a problem in personal wealth perception, where items like undershirts and white t-shirts were always going to be the same price; they will always feel cheap. Now, you can have wealth even when it looks like you don’t; a wealth so powerful that it resonates without any indication of why — you are wealth.
Anyone who simply “wears a white t-shirt” won’t have that empowered personal feeling of wealth. That’s why you have to buy Kanye’s $120 brand. It’s just enough that anyone could buy it if they really wanted to, but too much for anyone who isn’t rich to casually buy (like you would a white t-shirt).