That's a _feature_ for the telcos. They want you to be able to walk into a store, grab a new phone, and walk out several hundred dollars lighter with your old number already working on your shiny new phone. They want to make it as easy as possible to do that.

They never signed up to be the gatekeepers to your digital life, and there's nobody paying them to do that. Expecting them to make their sales experience worse than their competitors just because some bank or crypto exchange can't work out a decent way to authenticate their customers is insane.