That's part of creating the mystique. Disney wants MagicBands to be cool so guests clamor for them.
Besides, if Turkey Legs and Monorail announcements can have their own t-shirts, then why not MagicBands?
But they forgot that the mystique needs to be there first and then the t-shirts can follow. I wonder how many of those Limited Time Magic "Merchandise Truck t-shirts" they sold. Same stupid concept. Turkey legs and monorail were already popular before they got t-shirts.