Pretty sure you use an Instagram account to login to Threads, so that makes sense.
By that logic you’d have to delete your Google account if you want to delete any account for which you have used Google to login.
…do you not? To delete the data I mean, not just to make it appear deleted to everyone without access to the Google/Meta user database.
If you want to delete something that is part of your Google account, then yes. Like your Gmail address. But not if you want to delete your account in an entirely different service, that only uses Google for the login. I guess the problem is, that Threads is perceived (and maybe also marketed) as an independent service while it’s apparently just part of your Instagram account.
Except for the fact that they’re two different things and there’s no valid reason for not letting people keep one but not the other.
To many people, their Instagram account has become a big (and toxic, but that’s besides the point) part of their sense of self. To delete their Instagram would be to delete a significant part of their identity. Having to do that to get rid of Threads is emotional blackmail of the worst kind.