Back when eSIM was relatively new, while upgrading to a newer iPhone, my wife’s eSIM didn’t get transferred over but still got deactivated on the old phone.

And the T-Mobile Germany portal to download a new eSIM required authentication via SMS to that now deactivated number. That was fun. (As they didn’t have an alternative procedures to provision eSIMs in place, we had to go visit a store to get a new physical SIM first and could then convert that to eSIM.)

That's interesting that you can "convert" them. I kind of thought the whole point was there was some non-replicable internal secret that the carrier puts in there and that's why it had to be running on their hardware for so long, since they didn't trust your hardware to do that job.