Indeed, I think it's possible that the majority of people with degrees, have jobs that are not identical to their college major.

Certainly, most of us with unemployable majors. ;-)

Another phenomenon is employers applying the "engineer" title to any technical worker, such as designers, programmers, technicians, and so forth.

Part of it is that businesses evolve towards having caste systems. When this happens, then folks in the lower castes will try to rearrange their job titles to resemble the upper castes, or change jobs.