Originally Posted by
pattern_is_full
Yes - I asked that also.
A retired Boeing engineer here (tdracer) explained (my very rough summary) that the 757 was designed in and for a different economy (the 1980s). A very expensive aircraft to build and buy (although efficient with relatively low operating costs), in an era with no narrow-body competition from Airbus (yet). Once production ended in 2004, all the jigs and other dedicated production equipment were disposed of. So no economically-rational way to revive it when Boeing needed to compete with the A321neo.
With luck, he will be along to correct my "interpretation" of his words, where needed.
That's pretty accurate pattern... With the introduction of the 737-900 (Next Generation), it could do nearly everything a 757 could do (except for range), and cost
much less to buy. When Boeing made the decision to pull the plug on the 757, orders had dried up and the rate was down to one/month (while production officially ended in 2004, the decision was made in the aftermath of 9/11 - long lead parts mean it takes a couple years to wind down a production line). Since the 757 required a dedicated assembly line, that meant a huge amount of overhead to build one aircraft per month, while the 737 rate was approaching one aircraft
per day - spreading that factory overhead cost over a much larger number of aircraft.
The other problem for the 757 was that it had a huge wing - fine for the 180-220 passenger market, but trying to shrink it down for the 150-180 passenger market would have meant carrying far more wing than you needed - more weight, more drag, more costs (that's why 'shrinks' seldom work, while stretches usually do).
In the 2010 time-frame, Boeing was working on a new, clean sheet of paper replacement for the 737 (I had friends that were working it). But Airbus pretty much caught Boeing off-guard when they launched the A320 NEO. A new clean sheet design would have taken years longer to reach the market - then years more to bring the production rate up to the 40-50/month rate that the 737 and A320 series were at. It would have meant conceding nearly the entire single aisle market to Airbus for the better part of 10 year, while the 737 MAX could reach the market shortly after the NEO and the 737 rate was already in the 40-50/month range. With the benefit of 20-20 hindsight and the MAX fiasco, going with an all-new aircraft looks a lot better, but at the time the MAX was launched, it seemed like the best option.