Since in my lifetime I've only known calling everyone by their first name (except, like you say, teachers in childhood), I'm curious when the change occurred and how.
But yes, that notwithstanding, any period drama (Downtown Abbey) will give a good indication of this.
The change started in the '70s and it's not quite complete. More progressed in some regions than others. A couple decades ago, the manager at my first job was addressed as Mr. and it seemed quite natural to me at the time.
Please go drive through and visit Louisiana or Alabama at some point in your life. You'll find America has a lot of variance in it's cultural norms.
Not in isolation, but in full context there may be some practical merit. In the earlier age where these titles were used, women adopted their husband's entire name. A woman who married Mr. Robert Smith would become Mrs. Robert Smith. This provides feedback that her given name isn't Robert. Ms. Robert Smith would be ambiguous. Is her given name actually Robert or is she married to Robert? Who knows?
But, indeed, in the modern age nobody cares about titles. We have heavily curated Instagram feeds, or whatever it is the cool kids are into these days, to serve as a status indicator instead. That's the thing about status indicators: They only serve to display status for so long until it becomes commonplace and those with status have to move on to new indicators to stand out.