The beans used for iced coffee are mostly garbage
One roaster joked that cold brew is likely a large roaster's garbage disposal. It was an exaggeration, but there's plenty of truth to it.
An analogy our coffee scientist used was that you wouldn't use an incredible vintage to make wine coolers. Same goes for iced coffee. You're unlikely to see a special bean turn into a concentrated toddy because the process doesn't show the coffee at its full potential.
It gets worse for any mixed coffee drink (like the ones you see topped with whipped cream). Big roasters are likely over-extracting their beans in order to save as much on food costs as possible, since it's going to be loaded with sugar and milk anyway.
That said, there are roasters out there who take enormous pride in their iced coffee, going as far as kegging nitrogenated single origins. But that's the exception, not the rule.