What happens when the gubmint develops encryption software under another name, something like, oh, maybe “screwthensa” and makes it available to any and all? No one knows the gubmint was behind it. And the gubmint built in its own private entrance to said encryption software. Kind of a domestic Stuxnet.
If I thought of it, they have thought of it. Have they done it? I dunno.
That’s why nobody trusts anything but open source code.