Those "unadvanced" vehicles are among the most powerful AFVs of the SW galaxy: http://i12.photobucket.com/albums/a242/CptK/JuggernautsATAT.jpg And they don't suffer from "leg caught in cable"-syndrom, either. According to their history, immense distribution to remote forces during the CW, led to some Juggernaut-transports being lost or highjacked by the Separatists. Some of these could in turn have been picked up by the Rebels, years later, or be taken from Outer Rim Imperial garrisons.