The CITES ivory ban went a long way towards killing off ivory-based craft. It not only killed the physical buying and selling of ivory, but more importantly killed off the "feeling" about ivory amongst makers, dealers and collectors/buyers. Ivory handled knives are a liability (and sometimes a risk). They can't be freely transported across borders, some shows ban them (regardless of the status of the ivory), some dealers won't have anything to do with them, and some buyers shy away from them. For the knifemakers it therefore is just "easier" to use other handle materials.
Mammoth ivory was (is) an alternative, albeit a poor one, but often it has more character left untouched, so the incentive to scrim is further diminished.
Browsing the KNIVES annuals I also have to say that the standard of scrimshaw appears to have dropped somewhat. The real masters like Rick Fields, Bob Engnath, etc have sadly passed on to that great ivory tusk in the sky.
