The benefit of having knowledge embodied in a person rather than a book is skills; and skills deteriorate if not used; stockpiling human resources is a waste of time and money.
As for risk; show me the armies of those fired after the shuttle accidents. Even after Feynman exposed the dishonesty of the official reliability estimates, not a single bureaucrat lost his job for lying to Congress or the public about the risks (since the engineers had a good idea of the real risks, the management at NASA either knowingly lied or were effectively sticking their collective fingers in their ears and refusing to hear what the engineers said).
As for risk; show me the armies of those fired after the shuttle accidents. Even after Feynman exposed the dishonesty of the official reliability estimates, not a single bureaucrat lost his job for lying to Congress or the public about the risks (since the engineers had a good idea of the real risks, the management at NASA either knowingly lied or were effectively sticking their collective fingers in their ears and refusing to hear what the engineers said).