Sometimes the people who set up the email service just forget or don't bother to add the receivers email to the URL parameter when you click unsubscribe, so it'll ask for your email again which is always an annoying step.
That’s their mistake, and any other email I receive from them will be flagged as spam and sent to the junk folder.
I’m not in the business of fixing their mistakes for free.
I will click the unsubscribe link and that’s it.
Could be a way of saving computation, this way the email content is the exact same for everyone receiving it
It's a dark pattern which adds friction to the process, in order to reduce the number of unsubscribes.
I refuse to believe that “someone just forgot” to implement a user-friendly feature whose omission coincidentally benefits their company. It is not a coincidence, and it was not done unintentionally. The same way that it is not a coincidence that the “unsubscribe” link is always in six-point font the same color as the rest of the email footer. Code does not happen in a vacuum. Code does not get pushed to production without vetting and approval. As I say, the assumption of bad faith is baked in.