I missed that detail (it was illustrative and intended to be slightly humorous). A few that come to mind from my last few years:
- The modem in question is in the lower floors of a skyscraper. Nobody has good service. Incidentally, till wifi texting and calling became popular, that made forced SMS 2FA way more annoying than it already was -- run outside to catch a bar of service, try to get back to your apartment before the 2FA code expires.
- The modem in question is in the middle of nowhere (or some approximation thereof, like an hour or two out of Laramie WY). You technically have 50 kilobits per second of download throughput, but that's painful when the modem configuration app is 28 megabytes. It doesn't help that modern sites clock in at megabytes, and most of your software and hardware nowadays assumes anything over 10 seconds to a minute or so per request is a failure and times it out, making browsing some sites _literally_ impossible rather than just slow.
- You recently meddled with your APN settings and tweaked the one field that makes your phone helpfully decide to not display that APN entry, and it coincidentally means you don't have data service. Not having memorized 20 random ports and uris and stringly typed feature flags, you can't fix it without outside help.
- Your cell provider decided to increase your rates without notice when the contract renewed. You don't like being surprised by that sort of thing and had a spending cap on the card to prevent it, but you were instead surprised by a lack of cell service.
- Your cell provider's autopay functionality is broken the one day that year you needed it to work (friend's experience, not mine).
- Your cell provider had a bug double-counting data usage the one month you planned to get near the limit. Without internet you can't connect to their customer support to get that fixed (to their credit, customer support was fast and hassle-free).
- You're pinching pennies to get through college. You only have a phone because your bank won't let you in without SMS 2FA. It's only a smartphone because the cheapest of those are cheaper than the cheapest dumb phones nowadays (and you bought it used anyway). You don't have a data plan because that's an extravagent and unnecessary expense. (Why are you buying internet in this event? No clue, but it's another reason somebody might not have cell data, and I'm sure amongst the 3M people in the US with smartphones without a data plan some of them have self-consistent reasons for getting internet at home).
And so on. Any given day, lots of people have smartphones without data.