Somewhere at Sonic Team is a whole "roadmap of Sonic titles," says head honcho Takashi Iizuka, and the devs "think about which game to release in which year"

Sonic Team head Takashi Iizuka has explained how the studio plans out the releases of Sonic games on a roadmap internally.
IGN

Sega Addresses Concerns Sonic Racing: CrossWorlds Will Be Sold As a Game-Key Card on Nintendo Switch 2, Confirms The 'Full Base Game' Will Be Included On the 64GB Cartridge

Sonic Racing: CrossWorlds will be sold as a physical Nintendo Switch game with the "full base game" included on a 64GB cartridge. Switch 2 Game-Key Cards are physical cards that contain a key to ...