I wonder, though, if that's their reasoning, or if they'd rather have another complicated layer in place instead. It might just be mimicry - people doing illegal things have hired guns, and it seems to work reasonably well for them - without actually understanding why it works when expensive techniques (which they don't fully comprehend) fail.
I think that it has less to do with why the technical obstacles can be overcome and more to do with the fact that they can be overcome. Unless a technical obstacle can be 100% secure, having an additional layer of security in the form of armed gunmen is useful.
The layer of armed gunmen is obviously not 100% reliable either, but requires an entirely separate domain of skills/knowledge/resources to overcome than technical obstacles.
I've served in the military. We had an asset we needed to secure - not nukes, but fairly important. We did the risk analysis and wound up with this layered approach: big thick blast-, TEMPEST-, and EMP-resistant door, retinal scan identification system, and an armed guard ( enlisted, not contracted ) 24/7. There was other stuff too. I don't remember it all - it was 1996 fer cryin out loud.
Complicated systems fail in unpredictable ways, and we understood that. We absolutely did _not_ want to depend on technical means only.
Maybe some organizations behave the way you suggest, but IMHO it is far more rare than you think.
