HTURKAK, I believe that is how it originally was, but with all things, it morphed and changed. As society advanced and more things were being "engineered" other types of engineering (specialty) professions were born. So, the name civil stuck to what had been traditionally engineered (roads, dams, buildings, etc.) and new names were created for the new specialties, i.e. electrical and mechanical. A historic civil engineer would not have been involved with engineering electrical systems as electrical systems didn't exist. A historic civil engineer would have engineered limited mechanisms but nothing like what we have today which really started during the industrial revolution. Rather than use the blanket of civil to capture all of the new specialties (as a "civil" engineer was much more the norm than a "military" engineer by that time), society simply gave them new names.
That is at least my understanding of the history of the profession (and it's names)...