Didn't GOFAST/GIMBAL and the Nimitz tic-tac video leak? That could have given them convenient choices to look like they were cooperating.

Could they be covering something up? I can't say it's impossible.

I'm just saying that between the tendency towards overclassification, the UFO stigma, and seemingly legimitate counterintel concerns, it doesn't seem like this refusal is evidence of a cover-up in and of itself.