Boeing had a pretty good commercial team at the time, based in Seattle rather than Chicago, with of course extensive contacts with all their customers, and could see that demand for the 757 fell off a cliff after 9/11 and nobody was going to order more. BA actually started scrapping their fleet in 2000, many went for cargo even then because there was little secondhand demand. Remember that almost all 757s were ordered for sub-2,000nm operations, it was only later in their life that a fraction of the fleet got adapted for intercontinental work. The key thing by 2000 was that the A321 had come along, and quite a bit of this shorter haul demand got picked off by the 737-800/900 taking its market. Yes, these didn't have the performance of a rocket ship. They didn't have the costs of one either.