But you would need to somehow get in touch with said carrier. Granted, you could probably do that over WiFi but if my phone breaks when, say, I'm out camping I'm SoL.
My old phone is still logged in to Apple, still works, still holds a charge. I'd like some eSIM system that was as convenient as "phone dies, pull SIM, put in old phone, boot".
Now you might retort aha! See! In a very narrow set of circumstances.. let me cut you off, look, you're going to need to remember to bring a paperclip or sim tool to do it the old fashioned way anyhow. So you're remembering something. If you're an amnesic lost in the woods you got bigger problems.
Besides, those are 2 grams of weight savings in my ultra light backpacking setup!