If you think SEGA was going to keep their biggest in-house IP exclusive to mobile, for no sane reason (Nintendo got them in a contract) i dunno what to say. Eh... surprise? What sane business would go "Well, we released the mobile phone and its doing great. Cancel all other console games and keep this app up". Just doesn't make any sense what-so-ever, even if the game does 1 billion downloads and 60 million active users. SEGA would just grow that team and continue to hit other platforms for MORE money.
As its said, this game is being done mostly by the Mario & Sonic Olympic game developers while Sonic team heads are over seeing (including those Story Book devs).
So would you rather SEGA make more Mario & Sonic Olympic titles or have that small team support this game with more modes, characters, events and such?