Sega games on other consoles is far more cost-efficient, since they don't have to worry about competing with the other three consoles and two hand-helds out right now.

That and it's cheaper for gamers, they're more likely to buy a game if it's on a system they own, rather than having to buy an entirely new one from a company who's last console was an unfortunate failure outside of Japan.

EDIT : Sonic rox lolz