Don't underestimate the argument of "just to be on the safe side". Someone running a business who doesn't know a lot about cookies will often just put a banner on as an easy arse covering mechanism even when not required.
Perhaps someone could publish a clear A/B test on how many views/conversions you lose by having a cookie banner?
Or they had their site developed by an agency and the cookie banner is just part of their standard scaffolding for a new site.
Let businesses who don't know what they're doing be outcompeted by businesses who know what they're doing.