or better yet, accounts shouldn't be linked to the SIM in the first place. I really don't see the justification for it.
Signal's reasoning has evolved over the years, but their current excuse seems to be "it prevents spam."
But it's very possible to do phone number verification without making a number a primary identifier. And yeah, unlinking it would require remembering a password.
But to prevent sim swapping attacks, you need to remember a pin/password!