GrapheneOS is like a veteran and war zone expert: for them, not only the external environment is considered extremely hostile that you should leave your house only wearing an armor and with bodyguards, but also the internal environment is hostile: your bodyguards could be bribed and work against you, that's why you need to somehow be protected against that as well.

Just as physical security, digital security most of the time not as radical, and tradeoffs are usually accepted, especially when they are "invisible": hardware and software security features are usually not mentioned in the specs and the regular and even power user just don't know most of them and what do they do.

When GrapheneOS says "private" and "secure", they mean top-of-the-line security features, updates as soon as possible, all available mitigations against zero-days and insecure code which will limit the impact before the patch, etc. Security as in a killdozer.

When other say "private" and "secure", most of the time it means: "we've followed all the recommendations applicable to our development budget, device price point, and support life time". Graphene does not like that definition of these words.

For smartphone, chip manufacturer goal is not to protect the user at all costs, but to provide reasonable security features for the price.

BUT the goal of chip manufacturer to protect the device at all costs is for… game consoles! That's why Xbox, PlayStation, Switch all run on a custom silicon and not an ordinary chips!