And the said appliances were designed such that someone could open them up and repair them. An awful lot of modern ones can't be opened without doing irreparable damage to the casing, and once inside the fault is likely to turn out to be with a proprietary component (often a circuit board) which is unobtainable.
Not the whole story, especially with more complex* devices. The low failure rates of mass produced goods is a function of designed component and manufacturing processes that just weren't available decades ago. Most electronic devices were hand wired, and even if they had printed circuits, the component wires were hand formed, inserted into boards and hand soldered in place. Wires were cut at the time of assembly and dressed in place. Compare that with modern practice, - printed circuits are double sided, component selection programmed from tape bandaliers, surface mounted to boards with adhesives, solder paste and solder masks printed on the boards and the complete assembly soldered by heating the loaded board and flowing the solder in one operation. In those situations, rework is very disrupting, - unless the boards have a very high material/component cost, (unlikely on any consumer product), failed items are scrapped. So almost prefect first time yields are essential to the survival of the business.
So when these products fail in the home, there is little chance of effecting an economically viable repair, unless complete board assemblies are available for the exact model.
* in the context of its day.