I have four degrees, one of those part-time online. On-campus total is about 7 years. Somehow I got on the mailing list of the National Association of Scholars where my mailing label includes the honorific “Prof”. Maybe I gave them money or maybe I completed a survey, not sure what was the genesis.
I am familiar with this phenomenon.
Pharmaceutical companies sending mass-mailings to druggists always address them to "Dr. xxx."
The thinking is: If he's a dr., it will be correct. If he isn't a dr., it will be incorrect, but he'll be flattered."
I expect it's that way in lots of other lines of business, too.
Regards,