You can't have one without the other
Kirby Star Allies was a 2.5D, 4-player game that came to the Switch in 2018. While it will be looked back on as another great installment in the Kirby franchise, it’s actually quite meaningful to HAL. According to the game’s general director, Kirby Star Allies is directly tied to the creation of Kirby and the Forgotten Land.
Kirby Star Allies general director Shinya Kumazaki spoke to Nintendo Dream magazine about all things Kirby, and a discussion about Kirby Star Allies came up. Surprisingly, Kumazaki spoke on how challenges faced and met during Kirby Star Allies helped the team in the creation of Kirby and the Forgotten Land. You can read his comments on the matter below, via translation from NintendoEverything.
For the first fully 3D Kirby game, there were many challenges that needed to be overcome. One of those was overcome in our previous game Kirby Star Allies, which had been the culmination of a lot of hard work in 2D.
…we thought of it as laying the groundwork for future works and we were sure that the next game would be 3D. The Kirby team and particularly HAL Laboratory considered Star Allies and Forgotten Land to be a single large connected project.
…There were still things we were not able to achieve in Star Allies, and deriving from that we wanted to make a ‘deep and accessible fully 3D Kirby game’, while also continually rethinking the amazing traits of the ‘strange and surreal thing’ that is Kirby. And that became the theme for the game.