As many studies show, there are no completely disconnected OT segments, unfortunately. Likely, the hackers did not want to disrupt tech processes, but make easy money through ransom, isn't it true?
Yes, you are right. I see it in studies and I believe they just want to make easy money. However, here in Brazil we have already had more than 10 energy companies attacked in less than 1 year, there is a coordinated action taking place.
But here we still have old substations with old relays, which are not yet digitized. And networks really disconnected simply because they have not invested in this connectivity, with IT or the Internet for example. These are really disconnected networks, which helps to avoid a power outage.