I think the advocacy of ND oil was a belief that the detergents were not compatible with some parts in older engines. Once run on ND oil, engine deposits would come loose and promote leaks and other internal engine mayhem if switched to detergent oil.
The same fears were raised 50 years ago with the introduction of Mobil 1, especially destruction of engine seals.
And many freaked out at ARCO Graphite oil
My father did not trust multi-viscosity oils. Thought they would "gum up" his engines. He had various cars with straight 6 and straight 8 engines, He loved to use SAE 20 diesel oil that he would buy a 24 quart case for $6
The same fears were raised 50 years ago with the introduction of Mobil 1, especially destruction of engine seals.
And many freaked out at ARCO Graphite oil
My father did not trust multi-viscosity oils. Thought they would "gum up" his engines. He had various cars with straight 6 and straight 8 engines, He loved to use SAE 20 diesel oil that he would buy a 24 quart case for $6