My two cents....
Had many 60's - 70's cars, GM and Fords mostly with V8s. The oil change interval increase from around 2,000 miles in the early sixties to 7,500 miles in the mid 70's. The oil filters were large and stayed on for two oil changes. There was such a thing as regular and severe maintenance schedules but most people fit into the regular schedule. The common large spin on filter doesn't seem to have changed at all since then except for the silicone anti drain back valve and maybe the media is different. Engines last longer now. Engine, fuel, oil or carburation/fuel injection, I don't know why, but I would guess it's a combination of many things.
I agree that engines today last longer. No question about it. But as you mentioned, that can be attributed to much better unleaded gasoline, along with precise, computer controlled fuel injection, that provides the exact fuel / air charge regardless of engine temperature, humidity, engine load, or altitude.
Carburetors, along with automatic chokes, and the heavily leaded gasoline of the period, were basically horrible at accomplishing the same task. With many engines requiring "tune ups" in as few as every 8,000 to 10,000 miles. New spark plugs, rotor, condenser, distributor cap, and don't forget the "points", along with setting the "dwell".
Today you don't touch the plugs until at least 100,000 miles. Spin on oil filters haven't changed much, except for getting smaller, and more cheaply made. Yeah, the media might be slightly better at filtration.
But overall that is pretty meaningless when compared to everything else, along with much better synthetic lubricating oils. All of which contribute far more to long engine life, than the teacup sized oil filters of today.