Cookie banners would not be necessary if companies weren't trying to do shit with data, specifically personally-identifying data and personal-behavior data. If they were just running simple analytics over everyone, there would be no need for "cookie" banners, even as they used cookies. Instead, mainstream sites try to figure out my personal click paths and then associate that with a mail address I typed into their newsletter form accidentally but didn't click Submit on and then combine their data with data from millions of other websites assocuiated with the same email. The EU never said that all websites have to use blatantly non-compliant services from Google, Adobe, and tons of others.

Even the term "cookie banner" is a total misnomer here. "Extraneous and third-party data collection banner" would be much more honest, as cookies are a symptom but not an issue on their own.

This is not a failing of the GDPR. This is a failing of web designers, corporate marketing structures, and the legal system (specifically that of Ireland).