Testing and QC aspects of the process are necessary for PCB
Although inventors had versions of PCBs it was an Austrian engineer called Paul Eisler that's credited with allowing the printed circuit in 1936. Skip forward on the 1980's and boards became smaller and had more functionality as well as the production costs came down significantly due to capacity to mass generate the boards and components.
The truth that the circuit is on the fixed board offers uniformity to the design and thus finding and identifying problematic components is easier. Which means that they're much much better to fix and keep. And also this means the probability of making a mistake in rewiring is really a lot lower as the electronics come in a set place.