Why doesn't the repeat A-B feature work on some discs

Almost all features of DVD such as search, pause, and scan can be disabled by the disc, which can prevent the player from searching back to the beginning of a segment. If the player uses time search to repeat a segment, then a disc with fancy non-sequential title organization will not have timecode information the player needs to search. In many cases the authors don't even realize they have prevented the use of the repeat feature.