My guess is that it's because M1 uses esters in their products and consequently they won't pass the tougher oxidation limits found in the 2018 update.I don't believe any Mobil oil carries BMW's spec, the ESP 5W30 carries MB 229.52 but not LL-04 which seems unusual to me, I guess either Mobil doesn't find it important enough to pay to carry the BMW approval or there's some sort of rift between Mobil and BMW.