If I have to log in to a site to unsubscribe to emails, why shouldn’t I just block the email address instead?

Gmail is nice to try to conveniently unsubscribe from unwanted emails when you want to but it isn’t able to for some so I get frustrated because they’re for sites I’ve not looked at in a long time. I guess unsubscribing means I can avoid any incoming emails rather than just from a certain address.