It is often quoted because this is the correct definition of the word. The correct definition of the word Doctor is a person with a medical degree whose job is to treat people who are ill or hurt or a person who has the highest degree from a college or university this is why you do not get Doctors of plumbing or mechanical fitting, you cannot change the definition of a word unless you wish to take up the subject with the Cambridge University Press who define the word. Any one of the people who fall into the category below are engineers because to be an engineer you must meet just one of these criteria,
engineer (PERSON)
noun
1 a person whose job is to design or build machines, engines or electrical equipment, or things such as roads, railways or bridges, using scientific principles:
a civil engineer
a mechanical/structural engineer
a software engineer
2 a person whose job is to repair or control machines, engines or electrical equipment:
3 US an engine driver
engineer (PERSON)
noun
1 a person whose job is to design or build machines, engines or electrical equipment, or things such as roads, railways or bridges, using scientific principles:
a civil engineer
a mechanical/structural engineer
a software engineer
2 a person whose job is to repair or control machines, engines or electrical equipment:
3 US an engine driver