I'd say it is "also" has a lot to do with marketing and brand recognition.
Sales down Mobil?? Just think people go in ask for 5w20 Mobil, "Well miss/sir Mobil does not make a 5w20 they make a 0w........ That is all most people have to hear to go purchase some other brand. 0w what! does not even make sense.
I am sure in olil terms it does but not to joe public.
Like this post mentions, I am not disputing that it is a rebranded oil, but I am sure that marketing had lots of influence.