"Manufacturing jobs" doesn't mean doing the same job as in the 60s. Human productivity improves by offloading more to machines/tools/processes while having the humans manage other things. A human making cars now is not moving their limbs twice as fast as humans in the 60s, they're using tools that get the job done 3x faster than the person in the 60s. The jobs are actually quite different across time, but we colloquially call both "manufacturing jobs".