My opinion is that cookie banners are so bad because of GDPR and not getting rid of the cookie law when GDPR was enacted.
Then everybody kept their cookie banners around and folded GDPR requirements into it, making it more complex, and more necessary all over the place, and less likely for people to think do we need these cookies or not and do we need to show this banner because of fear of GDPR (potential fines are big!!)