They are sometimes required. Say you are on a mailing list for some company you gave your email to at some checkout counter one time, and you want to unsubscribe. You probably don't have an actual account with a login with that retailer, they just have your email address.
In this case, what alternative is there than having a magic link in the footer of that email that says "unsubscribe" that includes a token unique to that email address that acts as proof of owning an email account when you then click that link and ask to unsubscribe?