Your hiring practices, then, would miss a lot of good people. I can't show you any of the work I've done in the last decade, because it's proprietary, under NDA, and not distributed outside the company it was written for. Furthermore, I don't keep copies of it -- not only would that be a breach of my NDA, it would be completely unethical. All that I can do is show you my resume, and talk about what I did in general terms -- perhaps providing more specifics about the architecture of some sub-components. I'm hardly the only developer with such a background.

And, FWIW, just because I show you "other work I've done", doesn't mean I actually did it, any more than what's on my resume is true. I can show you a very efficient file copy routine I "wrote" the other day... if by wrote, you mean copied off the internet, but oops, I forgot to mention that when I showed it to you.