Oil is a big deal. And by that, I mean a manufacture definitely does not want to recommend something that could increase warranty claims, or worse, cause excess wear or deposits that cause an emissions failure. I've worked with a number of engine manufactures and witnessed a few oil tests. It's serious stuff. They might pay a 3rd party tens of thousands of dollars per engine to run durability. Or test 3 or 4 oils in house, across 50 or 100 engines per oil. It's not taken lightly! And then in engineering half the time whatever is on hand in a weight that's "close enough" gets dumped in test mules, because "that's what the customer is going to do anyway."