Nobody is killing mammoths for their ivory.
That is the reason for the ban on elephant ivory.
But this encourages bad behavior in regards to ivory IN GENERAL.
That is the point.
It’s not about the killing, they’re already dead Jim...so there is no source of new mammoth ivory making it a valuable paleontological asset that could disappear and so should be preserved; not cut up to hang from the ears of the modern day Marie Antoinette.