LogFAQs > #942203910

If Shadow is the Sonic equivalent of Venom, Infinite is Carnage. Shadow and Venom were introduced as darker, evil versions of Sonic and Spider-Man, but because they were so popular they stuck around, and eventually shifted towards an anti-hero / rival role. So a new character was needed to fill Shadow and Venom's old roles, who was even edgier with absolutely zero redeeming qualities. Enter Infinite and Carnage.

I hope Infinite comes back at some point, but I don't see it happening any time soon. Sega mandated that the Sonic comics aren't allowed to use Infinite, and he wasn't in Team Sonic Racing, so I'm guessing that they only intended him as a one-off, aside from being in Smash Ultimate as one of the weakest spirits in the game.