If I remember correctly, the maps aren't auto-updated by default; you do get notifications, but those are too easy to ignore (esp. since Maps is chatty in general).

And then for someone on an expensive metered or slow connection - which is a lot of people in the developing countries - they might not want auto-update at all. So if they didn't notice expiration, they'll find out that their maps aren't there next time they try to navigate offline.