That's not what that phrase means at all. "good enough for government work" is akin to "close enough", a reference to the half-assed nature of most government work.
Now picture such a thing without modern materials to keep dirt from falling on you. Granted, the floor is often hard pack dirt anyway and done well it's ok. But, again poor and minimally trained.
PS: Sure, if you where rich or competent you could go beyond that standard and there was plenty of high quality stuff made. But, the average farm house, private trail, foot bridge etc... was crap.
