It only gets upgraded if it was designed to be so upgraded, which adds cost/complexity. If you don't manage your backdoor before the probe leaves human hands, y

It only gets upgraded if it was designed to be so upgraded, which adds cost/complexity. If you don't manage your backdoor before the probe leaves human hands, you can't add it later. And, other mechanisms (some described in sibling threads) can help drive the risk of a backdoor very low, & the liklihood of any compromise being widely revealed (if ever exploited) very high.