Scarecrow was in the first film and made an appearance in the second
Sorry, should have explained my reasoning. Not a whole ton of people have seen Gotham Knight, to be honest, despite being relatively well done. Scarecrow showed up in the Dark Knight merely as a continuity nod to Batman Begins, and while Gotham Knight may be considered canon, the events that went on in it would be considered relatively obscure by most, and Croc showing up in The Dark Knight Rises might feel a bit odd and out of place. He doesn't really have the qualities necessary for a strong villain, unlike Scarecrow, who can stand up own his own as at least a semi-central villain. If Croc did show, it'd probably be for a very small portion of the movie, and even then, it might be hard to believe as a moviegoer. Besides, he was pretty much taken care of in Gotham Knight, if I'm correct.