With all the state-sponsored corporate & military espionage caused by China & Russia, with the never-ending probes from government agencies like the NSA/DHS/GCHQ/etc., with malware & ransomware attacks that can encrypt data in (generally) unbreakable forms, with criminal hacking organizations making off with millions of credit card numbers from retailers, with apparently no network controls as to how much data leaves company firewalls & where it goes, and so on, why aren't there more internal air-gapped networks in companies???
This has hit the point of absurdity. If you are working on military plane designs, working on your next corporate acquisition, or even making movies or music worth tens of millions of $$$, why would you put your prized, unreleased digital files on computers that have Internet access? What kind of batshit stupidity is that? What, so your employees can browse Facebook & check Outlook e-mail at the same time? Such an air-gapped network would easily become an island--one that doesn't need Windows Updates, can stay on an old service pack, gets no software updates that solves 2 problems and but makes a new one (e.g. we know the bugs), and the like. And if those employees really need their Outlook e-mail, IM, or the Inter-Webs where they work, they can have a 2nd very low-end PC, connected to the main network, with a KVM between the two. Might even increase efficiency, given the mind's inability to multitask well. Or give them freaking iPads on a wireless network that's not connected to their "sensitive" work computer.
It boggles the mind that given all these problems, which are increasing in frequency & cost every day, we still have little more than software firewalls & hardware routers between a company's most highly-sensitive assets (files & computers) and the big-bad-Wild-West-no-holds-barred-Internet.