****Why do you think they have to enclose chips in hermetically sealed “cans”?****
I know of no uses for hermetically sealed silicon. All industrial uses for pure silicon allow surface silicon dioxide, in fact count on it.
True, but the hermetically sealed enclosures are there to be sure that that same SiO2 layer remains the same thickness and continues to function according to design. An unprotected silicon surface, or one with an exposed SiO2 surface WILL oxidize, and the characteristics of the chip will change, or fail completely. The process may be fast or very slow (over decades of time), but it DOES happen.