post-launch support for online multiplayer games to me are more important for global sales than a "meaty single player experience".
that's what me (and you and other here and on other message boards) would prefer, but evidently it's not what the mass market is looking for, in an online multiplayer game
Splatoon, Mario Golf, Mario Tennis, Mario Strikers, Switch Sports...these are online multiplayer-focused games, that benefit a lot from ongoing support, in order to keep them still "relevant" in the eye of the consumers, keeping them active online (that's exactly their selling point)
even Mario Kart 8 started with the usual amount of tracks and no battle mode, and received full DLC, additional contents, now a brand new wave of DLC - that surely contributed to its sales-legs
if you are saying that they should have ALL the post-launch contents day one on the cart, and after that continue ALSO to develop and offer free contents for years...yes, it's ideal, but pretty unrealistic
listen, I'm not here saying that I love this approach, or that everybody should buy day one just trusting them to add "enough" contents; I'm simply saying that it's understandable for someone to wait-and-see what the added contents for free will be, while for others the core machanics of the gameplay and local + online multiplayer is enough and that for Nintendo a day-one purchase is not necessarily better than a purchase made 3 months later when they add a free Daisy DLC to Strikers, because this will bring a new wave of online players into the game, that will still have an active community