Third-party exclusives helped define the identity of the Playstation brand to a much greater extent than Sega or Nintendo platforms. Including a nod to that in the form of some prominent third party characters is pretty much a must for a game that calls itself 'Playstation All-Stars'. A person who understands PlayStation would know this.
And the final fantasy representative for this game is, ironically, from the first final fantasy game to go multiplatform away from the playstation.
When most think of third party "playstation all stars" they think of crash, spyro, lara craft, jill valentine/chris redfield, cloud/sephiroth, snake, etc. While expecting all of these characters might be a bit unreasonable, you think sony would've ensured at least some of these truly "all star" caliber characters were guaranteed to be available for the game.
A game like this is almost as much about fan service as it is about the gameplay itself, and sony is doing a very poor job of the former.