I think part of the problem is that Google has conflated the "mark as spam" button with "unsubscribe" and people just mash it as a shortcut to "make this email go away".

Most of the email that I get with an "unsubscribe" link is spam. It's not the user's problem that unethical companies decide "opt-out" is consent. It's not the user's problem that unethical companies take seconds to start spamming you but days to process an "unsubscribe" request. It's not the user's fault that companies regularly add new categories of spam users have to "opt out" from.

Unsubscribe is a trap, setting up a rule to mark every incoming email from a spamming company's domain as spam automatically is the only thing that works. Or tediously hitting the button manually, for nontechnical users.