Pretty understandable considering how many marketers and website developers don't know how to and/or don't care to make an unsubscribe button that works. Click a few dozen that make you type your email again (haven't they heard of tokens?), uncheck to unsubscribe from 20 different types of newsletter, find a bunch of email settings in your account settings, supposedly take 48 hours to take effect, have no effect at all, or the page doesn't even load, and you start to think it's easier to just hit "report spam" and move on with your day.

As I posted elsewhere on this thread, I'm inclined to think that if you don't have a clear unsubscribe button that works immediately with no extra effort, then you are spam.