Programs like this won't stay secret anyway - somebody is going to see a test flight in the distance, or an employee at a contractor will leak.
Announcing it gives the military a chance to control the narrative. If a photographer snaps a test flight and it appears on Gizmodo with the headline "Military testing secret drone swarms to kill us all", there'll be a massive public outcry, a huge negative PR cycle, possible a Congressional inquiry, and in the course of doing damage control the military will have to reveal more secrets than if they just announced the project in the first place.
Americans are not shy about inventing details when they have none, and also have a tendency not to trust either their government or the press.
Announcing it gives the military a chance to control the narrative. If a photographer snaps a test flight and it appears on Gizmodo with the headline "Military testing secret drone swarms to kill us all", there'll be a massive public outcry, a huge negative PR cycle, possible a Congressional inquiry, and in the course of doing damage control the military will have to reveal more secrets than if they just announced the project in the first place.
Americans are not shy about inventing details when they have none, and also have a tendency not to trust either their government or the press.