I assume it's because a business has different ideas about what to collect from their users and users are more or less willing to share some data with some spec

I assume it's because a business has different ideas about what to collect from their users and users are more or less willing to share some data with some specific businesses. Hence, every business needs their own consent rules. The fact that this is achieved with a cookie banner for 99,9% of all businesses is a side-effect. Could there be a better solution? Probably. But the law and the incentives aligned to cookie banner hell.