I think Square was originally intending to bring out the love story more, which is why seifer is on all the promotional images, but they were pressed for time or whatever.
I wouldn't be surprised if that were the case. I could never understand why Square would make him out to be one of the central characters, develop him early in the game, and then leave him alone. But the mushy Squall/Rinoa stuff trumps Seifer, I suppose.