When you go to a doctor, you expect that they completed training and are certified to practice medicine. It is the same for the engineering profession. Would you want to work in a high rise building that was designed and built some self-titled engineers who have never been appropriately trained?
In some countries it is that way. I know Canada is very strict about who can be called an engineer.
In the US, it is not that way. AFAIK, there's no legal definition of an engineer, and anybody can call themselves an engineer.
But that's only for actual Engineering disciplines. We in software don't need to take an "Engineer" test for the same reason we don't need to take a "Rock Star" test or "Ninja" test. We use the title as a courtesy, not an indication of qualification.
I believe you that this is the requirement for some fields of engineering. However, there are thousands of people reading HN with the job title 'software engineer' who did not take those exams.
Why would some national laws about certifications prevent you from referring to such a person as an engineer?
I left for software before sitting the PE, so they'd read the same were I to return to doing Mechanical Engineering work.
But of course it's silly to stand on principal on such things, so I've never taken offense to anybody calling themselves whatever they like. If the janitor can be an engineer, certainly anybody else can too.
I imagine Architects feel the same way. And Cardiologists will as well, when we start appropriating their title.
The PE thing really only applies to stuff like civil engineering projects.