My guess would be that the debut of the pipeline came right around the time that B&M was developing the inverted coaster and designing rides around the heartline of the riders. By rotating the track around the heartline of the riders, they demonstrated that the concept of the pipeline was unnecessary, and the same result could be accomplished in keeping with the 'traditional' track and trains with a different design approach, eliminating the problems caused by the excessive oversized track and heavy trains.
See Storm Runner, Colossos at Thorpe, Hydra, Speed Monster just to name a few of which incorporate elements from the Pipeline with traditional track and trains.
Just my guess - Dave