A band is not the same as a luxury fashion brand.

One is exploited by massive corporations, gets a single digit percentage of the profits they generate, gets known by word of mouth (or T-shirt) among fans, and creates a piece of culture.

The other is a (usually massive) corporation, exploits low paid workers, is a status symbol for the rich and the people who want to appear as rich, and sometimes they make an item that could technically be considered a piece of culture.

Advertising for and/or showing your support for them are very different things that imply different things, for different reasons.

Wearing band merch implies support for their musical stylings, a connection with the creative output of the band, and possibly their world view.

Wearing a logo-festooned piece of couture clothing implies wealth and status, and (often) complicity with sweat shops.

While the two previous paragraphs seem to be similar, because of the first two paragraphs, they are quite different.