It's all in the 'title'
In the UK there are two types of people - ordinary folks and "professionals" who are able to sign off official documents like passports.
The professionals, it has been deemed, are a very select, especially trustworthy group that include teachers, doctors and farmers ...
As a person, who did a degree and a year's teacher training course and qualified last year at 23, I could sign off that passport as a 'professional person'.
As a person who is 18 and has land given to them by the family and farms it, I could sign off that passport as a 'professional person'.
As a person with the same degree as the teacher, a Masters, 20 years in industry, 10 years running my own company and the same size piece of land as the farmer that's a landscape garden, I'm not "professional" because my face doesn't fit ...
The refusal of the badge "engineer" is in my view the same - snobbery of the term.
At the local FE college the (less than) civil engineers, who have never been out of the office and wouldn't recognise a bridge if you hit them with it, refuse to refer to the staff in the mechanical engineering department as 'engineers' because they do not pay to be part of a professional body and have a shiny badge ... The fact that the mechanical engineers could design and manufacture the equipment to build the civil engineer's bridge seems to escape them ...