Kun-rei has a learning cost and no one is paying for it. Hepburn or its close-enough "Ohtani" analogue is free due to (notoriously bad)compulsory English training as well as use of Romaji input on computers, and technical rule conformance to actual Hepburn is never questioned so it wins.
I don't know, I think the real sad part is that everyone knows the casual Hepburn from Romaji popularity; Kana shall be default from a nationalistic, purist, standpoint. Mazda and Ohtani are fine, certainly better than Zhang and Nguyen situation, which are supposed to be pronounced "chan" and "gwen" but being mostly sources of confusion.
I don't know, I think the real sad part is that everyone knows the casual Hepburn from Romaji popularity; Kana shall be default from a nationalistic, purist, standpoint. Mazda and Ohtani are fine, certainly better than Zhang and Nguyen situation, which are supposed to be pronounced "chan" and "gwen" but being mostly sources of confusion.