Why wouldn't the United States employ DARPA or the NSA to create a non-commercial mobile communications platform for high ranking government employees? Is signal in bed with the government? I must not be technical enough to understand the reasoning.
The problem is these officials chose not to use the secure systems, because they don't want those records to exist.
Because high ranking government employees don't want to be told they can't use whatever they're already familiar with for whatever they want, and they would rather heaven and earth move to accommodate them than be inconvenienced. Even if it exists, which is probably does, you can't force such people to use it, they'll just have you fired and maybe have the program axed for good measure.