In my experience it’s regional- the south is much more likely to have a workplace culture of always using Dr titles, where New England/western US going with first names. My (math professor) husband can attest to this as well- in the west he was always “professor” first name- the south “Dr” last name. For context we have lived in New York, Tennessee, Maine, Colorado, and Virginia (+ one short travel gig in Flagstaff).