Doesn't signal and whatsapp let a new user of the same phone number take over the account? Both will in some ways show that the keys have changed, but if you rent a number and then that is returned to the pool of rentable numbers then someone else can effectively stop your access to the account.

Tying accounts to phone numbers is a design decision that is just plain wrong for anything that does not only run on a phone or anything that is supposed to identify a person rather than a phone number.