Big Pistons Forever
It might be worthwhile remembering why Boeing launched the MAX.
Boeing didn't really want to do another 737 and was working on a completely new 737 replacement - I knew people who were on the program. But, when Airbus launched the A320 NEO series, it caught Boeing with their pants down. There were two major problems with launching a brand new 737 replacement to answer the NEO - first off Boeing was still struggling to get the initial 787 and 747-8 aircraft certified and into service - the engineering resources to launch an all new aircraft simply were not available. Second, launching a new aircraft means a bare minimum of 5 years from launch to entry into service - probably quite a bit longer (and that's without accounting for the engineering resource shortage). Worse, it takes time to ramp up the build rate of a new aircraft - and at the time they were pumping out 737's at over 2/day, a rate that would probably take another five years from EIS to achieve. So, basically conceding the massive single aisle market to Airbus for about 10 years. Now, ten years later with the benefit of 20-20 hindsight of what happened, that doesn't look so bad. But at the time, conceding that massive market - several thousand aircraft - to Airbus was simply unthinkable. Hence the scramble to come up with the MAX.