Ask HN: Why do email lists get spam signups?

I have a mail chimp signup on a side project site. I haven't added anything new to the site in over a year. All of a sudden I'm getting about one signup per day. If I google the email address most show up as being on a spam or blacklist.

Why do spammers sign up for lists? Seems like a waste of time and that they don't get anything out of it.