Wow, the mental gymnastics on this thread are really something.
The 737NG IS
an older version of the 737 MAX. This is exactly why Boeing got into this mess by quite literally pimping their 737 to the max.
And yet rarely is it ever brought up these days that the A320 and A330 are older versions of the A320neo and A330neo respectively, or how the 717 is the ultimate development of the DC-9, or how the 777X is basically a stretched 777 with newer engines and wing, or how the 747-400 is a new 747, or how the MD-11 is just a glorified DC-10-MAX
It's really strange that, even before the crashes, it was always the 737 MAX that got the bulk of criticism while the A320neo barely got any negativity at all. Yeah older original airframe (737 was 1960s and A320 was 1980s yada-yada-yada), but the 717 (and by extension the MD-80 and MD-90) were also extensions of ancient airframes but if anything A.net seemed to love (loved?) the 717.
The reason the 737 gets singled out is this:-
It seemed pretty clear from the outset that the fundamental architecture of the 737 platform was challenged by the "MAX" re-engine-ing in a way that the A32X NEO was not.
Subsequent events have borne that out in spectacular style.
That is not to say that any of the platform architecture issues on the MAX either were, or are, insurmountable.
But at some point the amount of manipulation required to solve the architecture problems begs the question whether a new airframe would have been a "better" answer.
Don't forget, Boeing themselves were already arguing the case for replacing the MAX, and were literally shanghaied into launching the MAX, against their better (technical) judgement by the success of the NEO - especially the AA breakthrough.
The A32X NEO was never challenged in that way, and was without question the right answer at the right time for Airbus.
That is the reason for the difference in behaviour.
My personal view is that, if Boeing hadn't felt so pressured to respond to the NEO, and had executed the changes (particularly around MCAS) in a more holistic and thorough manner, the MAX would still look like a good solution - it has sold a lot of frames, and is very efficient.
It can still be made to be a good solution.
Sadly the MCAS fiasco, and the two attendant crashes have fed the fire of those that thought it was a step too far for the 737.