Timing, as they say, is everything. Boeing (apparently) wanted to do the New Small Airplane back in 2010ish, and this would have replaced both the 737 and 757. They couldn't crack large volume composite curing (think they were hoping for cold cure technology), and then were forced to compete with Airbus for the massive AA order...which gave birth to the MAX. Had they had the composite technology they wanted, the outcome could have been very different. A 797-8/9 to replace the 757 and a 797-3/4/5 (or somesuch) to replace the 737...the A320 would now be looking old hat.