Websites want to make you believe it's only about cookies, but in fact it's about building a profile from your behavior. Often websites hold a live auction for the ads and others bid on your profile.
At shops like @Zalando you even agree that your email is uploaded to facebook.
Most websites ask for permission to send your activity to several ID companies (eg. Facebook, Google, Adobe or Xandr). Probably each of us has large profiles at 10-100 companies. There are even official marketplaces for profiles.
Advertisers build target audiences from those.
Behavioural profiles are often years old, because they get persistence from logins. When you delete your cookies, you are anonymous until you login on any page. Many websites share your IDs with others ("cookie matching"). After some clicks around everyone recognizes you again.
@rufposten And very often the "cookie popups" are intentionally misleading and manipulative (an example I stumbled upon just recently: https://unitedwestream.berlin/ - they first make it appear that the "bad" cookies are unchecked but then the button people will most likely click on because it's white will check the other two).
The old banners yes, but the new cookie walls are blocking only to force you to consent. This is a decision by the website owner. They aren't allowed to track you without consent so they trick you with dark patterns and nudging.
The more you decline, the more likely they will stop using them.
Interesting: there are some consultations at #eu level.
Look at this one:
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!