This seems like the inverse of the Doomsday machine - once anyone knows about it, it's useless. If I know I'm going to leave the country, I'll back up my phone

This seems like the inverse of the Doomsday machine - once anyone knows about it, it's useless. If I know I'm going to leave the country, I'll back up my phone to Google Drive (or wherever), factory reset my phone, and leave nothing for the investigators. If they'd kept this surveillance under wraps, they might have found something. Now, everyone knows to clear their phone before crossing the border (and the ones who don't know probably don't have anything worth finding on their phones). Of course, this could just be a tactic to increase queue times at the border.