See Point #2 in this two-month-old blog entry on Amsoil's website.Porsche2018, I agree with your previous suggestions regarding more frequent oil changes. I do that as well. However, that doesn't change the fact that Porsche has contradicting oil change intervals. All I'm seeking is some rational explanation as to why that is.
EU countries require a different type of oil than the U.S. does to extend service intervals and, thus, decrease the amount of discarded oil. The post includes some dated info, but I see corroborating evidence in several other places after a good ol' Google search.
Also evident: a push toward thinner oils such as 0W-16 for use in economy cars and hybrids, led by Honda and Toyota. The U.S. auto industry has apparently flat-out rejected the trend. Here's an article about that on Autonews.com, a semi-trade publication for the auto industry based in Detroit.
Longer service intervals between U.S. and EU vehicles appears to have been a 'thing' since at least the mid-2000s because of the stricter oil standards across the pond.