After all, from a privacy perspective it is still a disaster to create an account by using your phone number to sign in. From a typical user's perspective it is basically a worse version of WhatsApp that still cannot backup your texts and conversations properly, so why bother switching at all?
The users will still sit on WhatsApp due to the latter still being the case. Once your phone is lost, stolen, or you have a different phone, your conversations are lost if you are using Signal.
Oh dear.