I'd argue Mario Kart 8 was the one game that seemed to cause a bit of an uptick in sales even if it was a minor increase but that game has already arrived on the Switch long ago and done its part.
I also remember when Super Mario 3D World came out, it actually got a lot of positive press and praise. It was the same time the PS4 and XBOne launched and I think it was IGN that said SM3DW was Nintendo's secret weapon to combating the buzz of those released consoles because all they wanted to talk about it and post on twitter was stuff from that game compared to any of the launch titles for the new systems. In the end, it didn't really do anything to change the fortunes of the Wii U and, with a few years having passed since it was shiny and new, it's always felt like the majority of fans weren't really interested in this style of 3D Mario continuing. That's why you still had people hoping for a Galaxy 3 and it felt to me like there was a lot more excitement with Odyssey from when it was first briefly shown in the Switch reveal trailer because it promised less linear levels and more 3D exploration.
Compared to the 3D World reveal that seem to deflate people's enthusiasm who were waiting in anticipation to see the next 3D Mario, I don't think 3D World has ever really overcome that negative general perception even though reviews ended up being positive and a lot of people did like it. Odyssey, on the other hand, always had hype and positive reactions from it's reveal to its release which is part of the reason why it was able to move Switch systems on release compared to 3D World. If Nintendo had done a follow-up to 3D World on Switch, I don't think you see the same reaction or sales that Odyssey got and, in that regard, I agree with what Luigi Dude is saying. The majority of gamers didn't really care about 3D Mario multiplayer so that wasn't much of a draw in the end. Mario 64 and Galaxy are single player focused and that's what the fans want more. Even Sunshine seems to have more fans that the 3D Land/World style so it made the most sense for the series to return in that direction.
As for Ian's comments about the NSMB series, they've pretty much been taken apart already but I'l quickly add my two cents. Yes, I'm highly confident that I could distinguish which game was which from any screenshots one were to post or take between the four games. Even if you were to upgrade the graphics, as Brandonk Kong suggests, I still feel very confident I could distinguish between them. NSMB was pretty basic in its backgrounds while reusing a lot of SM64DS assets which helps distinguish it. NSMBWii had a lot of spinning ground in its game to distinguish it was well as more Super Mario World enemies and feel to the levels. Plus, different backgrounds. They've all got different backgrounds. NSMB2 should probably be the easiest of them all with its gold motif with gold enemies and so many coins in the levels. NSMBU has new enemies, power-ups and it seemed like it tried to have something different or visually new in each level to keep them unique and distinguishable a bit. Of course, it has some of the most unique backgrounds in the series.
The ultimate problem of the NSMB series isn't so much the visuals. It's the level design. To me, the series peaked with NSMBWii and the games after that felt really redundant. NSMBU took until about World 5 to reach levels that were more challenging and engaging. But half the game I felt kind of bored and had to push myself to keep playing because it just wasn't that challenging and felt kind of stale. NSMB2 seemed more designed for its coin rush mode and idea. Thus playing the levels on their own in the normal game mode also didn't inspire much enthusiasm as I progressed and it is the one game I probably remember the least of in the series but, thanks to the gold motif, I could probably still pick out screenshots easily. Nintendo did try some new ideas throughout the series but they still kept the level design pretty safe and didn't really try to change the formula up too much which is the biggest knock on those games and why New Super Luigi U may have been the best in the bunch because it did try something different and had more of a challenge. Of all the games, NSMBWii is the one I have felt like revisiting for some time so one of these days I may give it another spin to see how it compares but I feel like that and Luigi U were the best things worth playing in this series.