Since Threads is a separate app and logging in with Instagram was effectively a form of single sign on, it will be interesting to see how long this lasts.

It is unacceptable because it’s entirely intentional and avoidable, and in no way a best practice that benefits the users but instead the platform.

For the non technical - It’s interesting that a new profile can be generated from an Instagram account but all those fields are intentionally not being made to be removed.