Ubisoft's CEO Yves Guillemot has stated that he believes Mario + Rabbids: Sparks of Hope underperformed commercially because they released it too soon, only 5 years after the first game. He says that Nintendo advised Ubisoft to release Sparks of Hope on Nintendo's next console, because Nintendo themselves believe that a series should only get one main game per console, but Ubisoft declined that advice and designed Sparks of Hope for Switch instead of Nintendo's next console. 

https://www.videogameschronicle.com/news/nintendo-advised-ubisoft-to-hold-mario-rabbids-sequel-for-its-next-console/

They prolly should've conserved it I agree. I remember that even enjoying the first game. The 2nd game grabbed me with it's trailers but sadly, the scheduling of games they had that year was kinda packed so I never couldn't bring myself to buy the sequel l(yet ...)

They obviously would've won more benificing fromm buying one of the early releases on the next Nintendo console, simple as that

Interesting. It is an oddball kind of game so I wonder if, like Nintendo is suggesting, even fans of the game were kinda like thinking 'well I got that oddball experience in the first game I don't need it again on the same system'.

I bought Spars of Hope recently. First game was great. Won't get around to playing Sparks of Hope for a good long while though cuz of Zelda. But I for one am happy to have a second Mario+Rabbids to play through on the Switch, just too bad it didn't sell that great. Next gen I'd love to see a Zelda+Rabbids personally, rather than just a third Mario+Rabbids.

Shame cause it was much better than the first game and didn't get its just due.

It didn't matter when the game released, or on what platform. The game was basically broken due to the pathetically easy difficulty level.

I loved the first one, even though it itself was a bit on the easy side (once you'd upgraded your roster), but at least it had challenges in the form of the ultra stages and even rewarded you with finishing the stages with all 3 characters, which wasn't always a walk in the park.

If they were aiming the sequel at a much younger audience than the first then it would make some sense, but as far as I'm aware there was no shift in marketing to support this.

The only reason to keep playing was to see the world design, though this too, I thought, was a big downgrade on the first. Kingdom battle had a kind of toybox diorama aesthetic that really worked & seamlessly integrated the stages into the actual level design. Sparks of Hope on the other hand reverted to looking like most other generic 3rd person cartoony adventures & done away with the integration of the stages into the level.

I dunno what happened but many bad decisions were made & it was just baffling how little effort you had to put in to win a battle on even the hardest setting. What's the point of making a strategy game that is so easy that you don't have to emply any actual strategy?

But it's associated with Mario. Whether you look at mainline Mario games, or his many spin-offs, he gets more games per platform than any Nintendo IP. Only Pokémon comes closes or exceeds the number of games.
However, maybe Nintendo indeed would prefer 1 game per platform for a spin-off like this. Nintendo is insanely protective of their IP, and Mario+Rabbids is a very rare third-party game with Nintendo IPs.

Mario Party anyone?

Same with Splatoon.

Yeah, they ignored their own rule with Zelda as well, both Breath of the Wild and Tears of the Kingdom on Switch. 

Sparks of Hope is a really great game. I'm glad it was released.