Frankly, I don’t know. This thread is the first I’ve heard of it.
Carriers ask phone makers for config changes all the time. It’s possible this is a new capability that was requested by certain carriers.
To be fair, it’s also possible that the OP and I are misinterpreting what’s going on. For instance, iOS syncs your preferences across devices. Perhaps there’s some bug that’s causing the wrong setting to propagate back to this person’s phone because their iPads, etc are still set to allow “auto join”.
This happened in India. So one day mobile data was quite slow on my non-Apple phone. I asked my friend to enable hotspot on his iPhone. We were stumped when we couldn't find the "Personal Hotspot" option at all in ios settings. Called Apple support who informed us that Hotspot option is only available if the carrier enables it. They asked us to contact the carrier.
We were outraged and thought the carriers in India had suddenly decided to charge us extra for this option. Or maybe just for iPhone users. (In india, no carrier charges us extra for this option - and that is how it should be right? We are already paying more according to the bandwidth (3g/4g/5g speeds) and they also already limit how much data we can download. Imagine being charged extra for the "privilege" of sharing your data and consuming it faster!). We were prepared to yell at the carrier if they wanted more money from us for this but their customer support explained to us that this is a common complain they have with Apple iPhones, and all we needed to do was add some more info in the mobile data settings, which she provided us.
That's when we realised that it is a very American / Apple thing because the US business model of mobile phone and carriers are very different from India. In the US, most mobile phones are sold through the carriers and Apple and its competitors have to work with them closely. Whereas in India, consumers purchase their mobile phones independent of the carrier.
Every now and then, maybe every year or two, my iPhone says it needs to update mobile settings from the carrier. Fo those settings they asked you to change, it sounds like the Indian carriers probably could update them through that mechanism, or possibly that they were going to do so but hadn't got round to it yet.
That happens with indian carriers too. From what I understood, Indian carriers don't bother with the HotSpot settings because it is enabled by default for all users at their end. This works fine with Android phones but often not iPhones (in my personal experience).
> they’ve disabled the user’s ability to turn off “auto-join” on iOS
How (and why) is it even possible for carriers?