How would you know? Are you verifying them? SCADA systems weren't intended to be online, but that didn't stop critical infra for power plants, etc. to show up online. The convenience is too great to not try to remotely maintain them 'securely' & the assurance of airgaps is technical and expensive to get right.
Besides, are you considering the addition of modern AI to these 'offline' systems - factories, power, national weapons? You can get frontier models in a fraction of a rack today, who knows tomorrow. The organizations running these systems want in on the technological possibilities of AI, too.
Not to be a doomer about all this or anything, but there's a lot of evidence technologically superior entities dominate technologically inferior ones. So our home countries are in a Red Queen's Race to keep up, which is why adding "local" or "offline" AI to these systems seems probable. Again, airgaps are hard to maintain. It is within the realm of possibility that what's offline today is accidentally or intentionally networked tomorrow.