Boeing happened. boeing bought Mcdonnel Douglas and started to phase out the DC9/MD80 etc.
I had the rare opportunity to watch a brand new MD90 take off from KDCA...the sound level was so low, the pitch so high...it was magnificent.
I've piloted both the DC9 and the 737...no comparison...the DC9 is much nicer to fly, much quieter in the cockpit. Nicer on the controls.
while there is an advantage in the way the wing is loaded with engines on the wing, it is easily overcome by the beautiful, clean wing design, simpler leading and trailing edge devices as there is no engine to interrupt the flap.
I understand DELTA airlines is looking to buy every MD90 they can find as they have exceptional performance in some areas needed. Indeed, DELTA still flys more than 30 DC9's as they can find nothing that can truly replace them.
The DC9 series doesn't change pitch with power changes. IF you add power on a 737, the nose goes up, cut power and it goes down.
ITS all about money...and NO one on the ground has been sucked into a DC9's engines...but a number have been sucked into the 737's.