The 757 was, and is, just about as fuel efficient per seat mile as the NG 737 and 320. The reason it was never a huge seller was the airlines didn't like it for a different reason. When gas was cheap, labor and the cost of the airplane were much more than fuel. Getting high aircraft utilization was very important to keeps costs down. Turn around times were extremely important. In the end, Boeing sold a reasonable number of them, but over a very long time, so not a lot were built and delivered each month.
A big long tube with one isle needs more time to load and unload (cargo and bags as well). The airlines loved the 757 for what it could do, but didn't like it for the inefficiencies it caused in operation.
Fast forward 15-20 years. Now fuel is 40% of the cost structure, and turn around times less important. A few years ago Boeing couldn't give a 737-900 away, now they are selling well. 321's also never sold well in the N.A. market for some of the same reasons. They sold very well in Asia (not sure about Europe).
Besides shorter range for the 321 and 739, they are both ground loving machines. Very high V-speeds and runway requirements. In Asia most of the runways are long and at sea level. No problem. Europe and N.A. have a lot of old inner city airports with 2000' meter runways, or less. Not good when V1 and Vr are 173 knots.