Every place that puts a lot of people in close contact, whether it is a chip factory, nursing home, a meat packing plant, Amazon fulfillment facility, or a prison, is a hotbed for infection. Those that haven't seen a lot of infection yet simply haven't tested yet because they don't want to get people riled up by making them aware of it. The idea that hundreds and in some cases thousands of employees at meat packing plants are all "getting it at home" is ludicrous - why aren't people who work at grocery stores or Walmart getting infected at anywhere remotely close to the same rates as people in these dense workplaces?
Even if the guys on the fab floor are wearing the "bunny suits" which would presumably protect them better than about anyone they still have to change into/out of them somewhere where they will be near others doing the same, have cafeterias where they come into contact with a lot of people, and the entrance/exit process which might be a roadblock if they do a lot of security checks to insure people aren't smuggling secrets out or whatever.
If the government was on the ball they'd require all nursing homes, prisons, and any factory like facility where hundreds or thousands of people are in close contact daily to test everyone and publicly report their numbers. You can't make accurate decisions without accurate and current data.