It is part & parcel with the expanding universe.
Back when the universe was about half its present diameter, we called them "Mister"; and even the few PhDs at the community college were called simply "Doctor".
Professors...actual holders of a chair...were highly insulted, and let one know it, if one addressed them as "Doctor" rather than "Professor"; and they jealously guarded the term from upstart encroachers.
To put "Professor" in the first line of his official campus bio would have been a declaration of war upon the administration.
His stated official rank is Adjunct Instructor; not even full instructor.
Ah, I think I misunderstood the source of this bio - I thought it was something that the university had written. It is tacky for this guy to call himself "Professor", although it might be courteous for others to do so.
Even though etiquette is more relaxed now I was always careful not to refer to myself as "Dr." or "Professor" when I was a non-Ph.D. lecturer (and I corrected people when they called me either of those).