[tptacek]

Many (maybe most? I don't specialize here) backdoors are deniably accidental, a term I'm coining here to mean "could be sabotage, could be a development artifact".

Whether any of those backdoors are deliberate is much less relevant than whether they're known to your adversaries. In the case of Chinese electronics engineering, your adversaries have the blueprints.

Do you really think it's likely that designers of bespoke silicon reliably decap, image, and analyze the finished products? I think you're attributing Intel/AMD-level wherewithal when, just like in software, a huge chunk of the market has nothing resembling the resources of the leading vendors.