It's like saying Michelin-starred restaurants are a commodity.
They aren't.
Once they are on that list they might be sort of interchangeable to a specific sort of person who just wants a generic "nice" restaurant and picks one off the list when they get to a city.
But they're all unique and different in really substantive ways, and also different from non-Michelin starred restaurants.
Your example of venues that hosts bluegrass works the same way. You trust the guy who books the bluegrass bands. If they just offered a gig to every band that asked you would hate going there and they'd close soon. Have you seen genuinely bad bluegrass? You don't like it, I can assure you of that.
You're just talking about curation. And the fact that curation is even possible proves what I'm saying.
If recorded music was a commodity there would only be one playlist because you would not be able to tell one playlist from the other.
Can your car tell Exxon from Sunoco? Can you drink a glass of milk and know which dairy it came from? Of course you can't.
THAT is what a commodity looks like.