Something I wrote back in 2005 in an Email to a friend in Pittsburgh with whom I share musical tastes...
I wrote:
OK... Drive-By Truckers Story. Now on the last day of school, someone came in wearing a Drive-By Truckers T-shirt. Now, you would think if someone went out and bought a band's T-shirt, they'd like the band - or at minimum have heard of the band? Think again. Welcome to NKHS. So our English teacher had the nerve to question this guy, "Who are the Drive-By Truckers?"
To answer her question, the guy shrugs his shoulders and shakes his head: "I don't know." The irony is that if this guy is a classic rock nut like everyone else, I would think he would LIKE the drive-by truckers. And I am 97% certain he is a classic rock nut.
Actually the guy who wore the DBT shirt was a total Deadhead - he would have loved the Drive-By Truckers certainly. A 97% chance misses too low.
So I can, from experience, understand what you're saying. People wear band T-shirts just because it's what Society dictates they do.