because the dodo business class is for things like having people over to visit npcs and having ppl water your flowers for better chances at a hybrids while nook's cranny is for specifically buying, selling, and trading items.
I think the business class is more for inviting people to meteor showers, or if someone is crafting on your island, or stuff like that. Not so much for selling items but for EXPERIENCES.
...That being said, I'm still kinda new here, so I could be way off But so far I've only done those kinda things in DBC
(that... that's an abbreviation people use, right?)
Dodo Business Class was created because people were charging a fee for others to visit their islands. So basically The Airport board is for free visits, and the Dodo Business Class board is for people who want to charge an entry fee to go to their town for something.
Nook's Cranny is strictly for buying/selling/trading in-game islands, not visiting people.