You also must think its a marketing thing to. Mobil 1 is good yes, they also have market share and brand recognition. There may also be some money paid to use it as a factory fill by Mobil.
Another thought is that would you want to buy a corvette factory filled with O'rileys oil. NOt saying its not good but this is the first tthat most of us had heard of it, and if your buying a 50-60K (no idea what they cost) corvette would you want it filled with some oil you have never heard of? I dont think they would sell well or people would also wonder what else Government Motors cheaped out on!