Air gapping is often "good enough" protection for all but the most sensitive and desirable targets, even if people plug things into them all the time. An air-gapped PC might get a virus that way, which could be damaging in some way, but it's not something that most companies need to worry about.

A counter-example is something like Stuxnet; that likely leapt an air gap, but it was exquisitely targeted for that scenario. I'd worry about this as a nuclear component manufacturer.