I thought it wasn't so much the saving money as the being quicker to market a jet that competed in an expanding new marketplace for more efficient, quieter, cheaper to run, mid-sized carriers, to replace a fleet operating out of provincial terminals which were mostly still operating with fixed height embarkation steps rather than the full-range height adjustable jet bridges of larger hub terminals. They had shorter landing gear struts in order to get the plane to sit lower down, which limited the range of engines their airframe could carry, and had previously adjusted the engine shape, squashing the bottom flat to make it fit. The engines they needed to compete with other manufacturer's planes were bigger and rounder, too big and round to actually fit safely on the plane where they were supposed to. To go into a full development cycle for a new airframe able to lift these bigger, rounder engines clear of the ground whilst still keeping the door heights the same would have taken many years and billions of dollars. By mounting the engines in a different place on the wing, they could make it work with an existing airframe for which existing terminal infrastructure was present. But by doing that, they f***ed up the handling, which they tried fixing in software.
Methinks it would have been cheaper to just supply every airport that needed them with a new set of boarding stairs/lifts.