I think it is just because there are not many divers who are knive people; 'least I have never known any, except pretty serious ex-mil folks & LE/SAR people. Most sport divers just don't know and don't care. Not many folks will take a Randall 16 out on a reef.

For example, I am the only one I ever saw on a recreational dive that carried two knives, except for a legendary Mexican guide named Martine.