Having worked at large companies before, I'm almost certain that more than one person working on the product raised the point "this has a microphone, why isn't it documented?" or "this has privacy implications", but was silenced. (Or it could be that everyone working at Google has been carefully chosen to not have such concerns; I do get that feeling sometimes too.)
Contrast this to Amazon: during design of the original Echo at Lab126, an engineering discussion took place where they determined that implementing the mute function in software would be less expensive in terms of component requirements than implementing a physical disconnect of the mic circuit. The engineering team refused to take the less expensive route, and insisted that the mute button physically disconnect the…
Update to clarify reasons for this characterization: Parent used the words "refused" and "insisted," which strongly suggest conflict between the pro-privacy engineers and others at Amazon involved in the project. And "so that no future engineering team could decide to stealth 'unmute'" suggests a lack of trust in long-term company management. Nothing in this story supports the later statement that "Privacy of customer data is considered the most important thing to Amazon."