How do we know that they did 1080p scans of the films back in the early 2000's? All that we know is that Paramount, at most, scanned them with HD Broadcast standards in mind (especially since at the time there was nothing for Blu-Ray or HD-DVD, and DVHS was barely making an impact). So for Paramount doing even just a 720p transfer in the early 2000's would've been sufficient, as far as they were concerned.