This may or may not be a surprise to you, depending on your level of cynicism about the relative lack of content in Ridge Racer for PlayStation Vita, but it was developed at a quick pace. A Famitsu interview with director Hideo Teramoto (translated by Andriasang) notes that development started in "spring," which likely refers to March at the earliest -- giving the team about eight months to have the game ready for the Vita's Japanese launch.
Teramoto said that the development schedule was "tight," as Andriasang puts it, but that the Vita hardware was easy to develop for, with the development kit in an "advanced state." The content was in an advanced state as well, on account of having already been designed for other Ridge Racer games. Oh, there we go being cynical again.