I remember it used to be quite common to install an OS and not have internet access. The OS simply lacked the correct LAN or WAN driver; alternatively one might be setting up an OS during an outage.
What would you even do with a PC that never has internet access? (apart from controlling some machinery maybe).
This is actually a massive use-case. Basically every piece of heavy machinery is using the OS it shipped with. Those systems naturally are forbidden from connecting to the internet but happily plug away at their job.
Legacy software in general is a great reason; retro gaming on period-appropriate hardware and OS, for example.