The problem with the military using an off the shelf system like Signal isn't the tangible features (re: encryption, usable ux). The problem is one of control. What happens when the government gets into a dispute with Signal (say, over a warrantless wiretap) and Signal decides in protest that it will no longer have any DoD affiliated customers? What happens when, through a series of shell companies and legal loopholes, a controlling stake in Signal ends up in Chinese or Russian hands?
From the PoV of the DoD, owning the system from end to end is a feature they shouldn't compromise on, even if the other features suffer and it costs more than it otherwise would.
The problem with the military using an off the shelf system like Signal isn't the tangible features (re: encryption, usable ux). The problem is one of control. What happens when the government gets into a dispute with Signal (say, over a warrantless wiretap) and Signal decides in protest that it will no longer have any DoD affiliated customers? What happens when, through a series of shell companies and legal loopholes, a controlling stake in Signal ends up in Chinese or Russian hands?
From the PoV of the DoD, owning the system from end to end is a feature they shouldn't compromise on, even if the other features suffer and it costs more than it otherwise would.