Security and privacy are not Apple's singular goal. They are also making computing devices that they think people will want to use.
So yes. If Apple were serious about protecting privacy and didn't care about anything else, then the rest of what you say would follow.
In some ways, Apple's goals are in conflict with each other. The most secure system would be self-contained, and walled off completely from the outside world. No cloud, no WiFi, no email, no messaging, no internet at all. But who would want such a system? (Darn few, to answer my own question.)
On the other hand, security and privacy are absolutely not, and cannot be, marketing BS as you call it. Every time Apple's privacy mechanisms get breached, Apple takes a PR hit, and people like you make sure that is the case.
In order to be an effective personal assistant, Siri needs to know a lot about you. But when Siri and Alexa and Cortana are sitting on the park bench by the playground, Siri also needs to be discrete. No gossiping about things you told Siri in confidence. And whatever records Siri keeps to stay on top of your busy schedule need to be kept safe, in case Google Now comes snooping around her office, or PRISM or Echelon or GhostNet, for that matter.
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Also, doctors, clergy, teachers, and astronauts.