Earlier quoted context omitted.
I will avoid getting into a “who understands economics better” debate. But factory workers usually require specialized machinery, tooling, and physical capacity, which makes overhiring slower, harder and more constrained. Those investments force more deliberate planning. By contrast, engineers mostly require a laptop and company hoodie... That low marginal cost makes it far easier to hire aggressively on expectations…
Factory overhiring can happen easily by adding speculative 2nd and 3rd shifts. No need for extra equipment, tooling, or physical capacity. Lines with specialty equipment and tooling can also often be sped up. That can allow for other jobs to be added to all the functions that support the processes involved before and after the specialty equipment. New employees also often require training and some apprenticeship time…
My experience with seeing new shifts added is initially with only specific processes, and even with those it is with journeyman level technicians running a small crew to support relieving a bottleneck in production.
Alternatively, manufacturers can outsource until they have enough volume to add a shift, but across the economy the net is just transferring production from one facility to another.