My thought is this...if you can find any additive that could reduce to coefficient of friction successfully it would be wildly sought after by every bearing and petroleum company in the business. This represents a global group of cutthroat billionaires who would kill each other to get this "magic" formula and patent it. Sorry, it hasn't happened yet. All oil additives that make these claims are a waste of money. Your efforts and money are better spent finding a better oil and not adding any "snake oil" to the mix.
That seems to settle the question nicely.
Is it possible that some additives have qualities that an oil formulator might find unattractive, even if they were desirable from a strict engineering perspective? For example, an additive that turns your oil black, or requires that you shake well before using.
Or, perhaps an oil company determines [correctly] that their oil will last one oil change interval, provide adequate lubrication and is profitable to make. That same oil with some additional additive might last longer than one oil change interval, might provide better lubrication but would be less profitable to make. As a corporate person, which would you choose to make?
I have used the Liqui Moly products...useless.
Which product(s) are useless? The Liqui Moly folks make a wide variety of products, many of which are certified by BMW, Mercedes, Porsche, Renault, Citroen, Peugeot, ILSAC, etc - the list is quite impressive. Are those products useless as well?
BTW, some Liqui-Moly motor oil products contain MoS2, a well-known additive which they also market separately as Liqui-Moly Anti Friction. Are the oils containing this additive useless? If the additive is worthwhile when included in the Liqui-Moly motor oil formulation (which oil is certified by ... see list above], then is the additive worthless if added to some other brand of oil?