The economics against a cord board were/are huge. With these there is a very large number of mechanical parts that could and would wear out over time. With electronic systems most of the mechanics at the board were replaced by electronics inside the PBX. And the electronics didn't have the "wear and tear" of the board. The switch board console turned into a relatively cheap (compared to a cord board) device. So if it broke you'd typically just replace the entire thing. Maybe with a credit for the old unit which would be repaired at a depot and put back on the shelf as a repair part.
So the entire economics of the sale and ongoing operations changed. Which upset a lot of sales plans, sales reps, service contracts, and union technicians. Which is why much of the savings customers might expect with the new technology takes years to show up. Sometimes it takes a generation for the old staff to "age" out and some times it takes a new entrant without a past before the economics change. In computers mini-computers did this to mainframes and PCs did it to both. Much of IBM's problems of the 80s and 90s were caused by the inability of the existing work force to adapt to these new economics. Ditto the airlines and deregulation.