In the U.S., the CAN-SPAM act requires companies to honor your opt out/unsubscribe request within 10 days. For particularly agressive mailing lists that don't honor unsubscribes I will happily report them as spam to my email provider, report them to the FTC, and send a cease and desist letter I generated with chatGPT to their legal@example.com mailbox.
Some people do it as a political statement. Blocking Israel is a real example I've seen.