I think this article solves for me the mystery of why NAB would buy the diners brand and shut it down without offering a pathway for retail/business customers:
[URL unfurl="true"]https://www.capitalbrief.com/article/remember-diners-club-nab-is-finally-killing-off-the-storied-credit-card-63038900-753e-4e33-b63a-4ebb2e49856c/preview/[/URL]
It turns out that they scored a massive whole of govt contract previously with Diners out of the purchase, shifted them to their commodity visa card offering and let the rest die. So perhaps NAB aren't as crazy as they seemed.