Why didn't Ventus get a prototype Keyblade in BBS?

In BBS, Terra and Aqua started off with smaller, less powerful Keyblades based on the ones they had in the KH2 secret ending, with them getting access to those latter Keyblades near the end of the game. Ventus, meanwhile, had the Keyblade shown in the secret ending from the start, and never gets an upgraded Keyblade in the same style. Why did Ventus not get the same treatment that the other two did, and why give Terra and Aqua prototype Keyblades if they couldn't do the same to Ventus?