That users reply to a mail and type out a lengthy message about not wanting to receive further mails like it instead of clicking the obviously visible unsubscription link.
Unsubsribe links don’t provide them the satisfaction of berating you for (a) sending them the unsolicited email or (2) them signing up in the first place and forgetting about it, thus believing it was (a).
I know you how you feel. About 50 times a day, I know. My subscribers make sure of that.