Good point. In addition, we know that most radios had to suffer some of the worst maintenance conditions, temperature and humidity variations throughout the world, not to mention being frequently raised in temperature inside their often closed in cabinets. Not exactly the best conditions, and yet most equipment still operated for decades, and some even to this day.
Surely engineers anticipated such harsh conditions and designed accordingly.
It appears that it is more likely that construction quality, and material choices are most directly responsible for long term failures.