Well....
Carol Merrill wasn't the one who had to bear the manufacturing costs of turnaround shelves, and GE really needed to stay competitive in the heated-up appliance market of the 1960s. Those turnarounds cost some serious money, and they weren't universally beloved, anyway - anyone who got to clean up a major spill on them got pretty resentful by the time they got all the gook out of the crevices, both topside and bottomside.
Don't get me wrong - I was around those shelves for years, and nothing will ever beat them for sheer convenience. But I can see why GE felt they were no longer necessary after a certain point.