At some point Doctor, Engineer, Accountant became titles linked to a formal qualification why not teacher?
I see this thrown around a lot but it simply isn't true.
It's possible to be an accountant or an engineer without formal training. The type of work you can do is limited by legislation before you have to be part of a professional body; i.e. a Chartered Accountant. You have to actually be a Chartered Accountant to call yourself one, but there are plenty of good accountants out there that are Accountants and considered QBE (qualified by experience).
My understanding is that engineering is the same.