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”.