Does iOS have any way of telling if you’re on an unlimited data plan? If not, maybe it’s just to prevent the footgun (and subsequent bad PR) of somebody accidentally updating the OS over an expensive metered connection. But it could also be a carrier demand, not really sure.
Mine doesn't have this either (Europe), and I have unlimited data too. I have a "Data Plan" setting under "Mobile Data", which is not activated, so I'm guessing that setting is only there if your provider gives you a data plan that Apple recognises.
