Basically only web apps can do CD

CD == Continuous Delivery, which can also mean publishing a new "release candidate" artifact. Maybe there is a more stringent QA system downstream, such as QA teams after a car gets a firmware update to that release candidate.

A lot of enterprise and industry software [...] have stringent vetting procedures that mean they can spend months verifying and approving a new major version before upgrading

This happens on the consumer side too, with risk averse customers, even if they adopt a continuous delivery paradigm upstream. It's also a common argument against a rapid release model, but is often dismantled when appropriate, automated safeguards are put in place. Not always possible to automate everything, due to regulations, but automating the bulk of the tests are in everyone's best interests.

How are those tests triggered? On developer machines? Not very reliable that a human will remember to execute them, even if it was possible to run them all from a workstation. That's why there's a bastion host or, hopefully, set of hosts to run those tests and builds. That's the CI/CD system. That's the value.