It was a necessary part of the manufacturer’s wartime job to take out ads explaining why their products might not be available. Not only did this spread a little advertising money around, it kept the product in the public mind for the duration - and reminded customers that Scovill was doing their part like everyone else.
If by change the customer had never heard of Gripper fasteners and was thus compelled to seek them out . . . why, that would be fine. too.