More than likely because it's not all that impressive in the common flavors, like 5w30.
Meets the API limit, which, IIRC is 15% for most common grades.
By how much it beats that limit is a guess, but I'd guess that if M1 were way below the NOACK limit, like 10% or less, they'd have it posted in their PDSs for all the world of BITOG to see.