Soul Calibur 2 sold more on the Gamecube (Go Link!) than the PS2 or Xbox versions, and the PS2 exclusive SC3 sold *considerably* less than all 3 incarnations of SC2 combined, IIRC.
It's a distinct possibility that Sony had a hand in it. Of course that's just a theory, but still a sound one.
Nobody is crazy enough to accuse me of being sane.