Yes - you're right it's just because it had XIII in the title.

I'm sure the fact that most of it's pre-release material looked rather camp and girly - following on from the only other numbered sequel that was X-2 being exactly that had nothing to do with consumers shying away from it either.

I'm also sure the relatively short development turn around time by Square Enix standards didn't cause people to question whether this would be a rushed half-assed title or not.

I'm sure peoples perceptions of previous "spin-off" titles such as the FFVII compilation didn't influence their decision either.

I'm sure it's launch window had nothing to do with it either.