Originally Posted by
procede
With a narrowbody, the fuselage would be so long, it would mean a heavy structure to counteract the bending and also very high and/or complex main gear to not have a tail strike on takeoff and landing and still get to an appropriate angle of attack. Going to 2-3-2, like the 767, you are adding a aisle for a single extra chair per row. Aisles do no generate revenue, but do add volume (drag) and weight, making the aircraft increasing the cost per seat.
The 757-300 and the DC8-61/63 called, they beg to differ on the single aisle length. Pretty similar length both of them.