Although we did not share numbers, Sega had previously indicated that Sonic Superstars sales were lower than expected, and the company recently commented on this performance, saying that the game was released in October alongside a number of competing genre games.
The competing game that immediately comes to mind is Super Mario Bros. Wonder, which achieved tremendous success on the commercial and media levels, breaking the 12 million copies barrier, with Nintendo indicating that the game is the fastest selling game in the history of the series.