There's got to be a reason why oil is both a never ending and a fascinating issue. My take on it is that is that no one is ever entirely sure they're right, and there is always this little nagging doubt at the back of their minds.
My guess is that most people who can't figure what part the hammer fits into the age old hammer, nail and lumber problem can change the oil on a bike. Then the problem gets down to what do I put into that oil filler thing. An enigma wrapped up in a conundrum Then comes the part that most people have issues with, reading the owners manual. Then comes the sticky part, which oil has the specs the manufacturer recommends and does it have to be exactly what the manufacturer recommends? Last but not least, greed. Will el cheapo work versus do I want to risk my baby by using that? It's a complex question that plays with our simple minds