There is definitely a punitive cost for sending emails that are repeatedly marked as spam though. You also can’t just cycle IPs because a brand new IP with zero sender reputation is treated with almost as much suspicion by the big player as one that is known to be a spammer.
It’s much better to give people an option to opt out, and to honour it. Most of the email sending providers (e.g., SendGrid, mailchimp, etc) force you to include the link and automatically block future sending to that address. Some will even provide you the option to provide a reason, where you can specify “I did not sign up for this” which in sufficient number will flag the sender account. I suspect the vast majority of cases where people unsubscribe but continue to get email is actually some incompetence from not having multiple disparate email systems sync back to a shared do not contact list (rather each system is maintaining its own).
Click the unsubscribe button.