Well, there is the simple answer: "Because it's their first PS2 game."
If you look at all of the HD Collections and such that have been coming out on PS3 lately, they're all old PS2 games. Re-releasing PS2 games (sometimes in bundles) with graphics updated for the PS3's HD graphical output is a big fad, recently, for whatever reason. As such, if SE is to follow suit, they would *also* re-release a PS2 game.
And, in that case, the only other option would be XII, which would make even less sense. I don't know why everyone is releasing PS2 remasterings lately - it might be a Sony marketing thing - but there it is, that's what they're doing. sweatdrop