With pre-rendered maps, the level of detail etc can be tweaked so everything looks good at each zoom level. Considering the BF was almost cut from the game due to time constraints, it is possible they were not able to create the additional sized images of each map element, to allow for zooming in the BF. Since the game engine was not originally designed with random maps in mind, perhaps there were problems updating the automap to handle the BF, which could not be resolved in a reasonable amount of time.
