At least from my few years in the automotive manufacturing, production engineering is looking for ways to make assembly go smoother. Depending on the organization production is supposed to know enough about the design function not to mess it up. I don't know what was done in the '70s. In the later '80s, the production pieces had to go through the same battery of tests that the design validization units went through.
All that is to say that the extra connectors must have seemed adequate at the time.
Did any company not use bulkhead multi-connectors at the time? Imagine having two dozen wires coming through grommets with in line connectors. They'ld be flopping around the engine bay and a even a bigger PIA for troubleshooting and repair.