The original 2010 release of the game for the Nintendo Wii and DS systems, was intended as a single experience split between 2 systems. You could play each half as its own game, but more dedicated fans could play both versions for nearly twice as many levels, an expanded story, and all around a more "complete" game experience. This makes the 2021 remaster "Sonic Colors: Ultimate" excluding all of the DS content a strange decision, especially considering its "Ultimate" sub-title, as it's essentially half of the original release.