I don’t really have a problem with this (as you mention, stores have had their own brands forever), but you may be interested to know that not all Amazon brands are clearly marked and there are a lot of them: https://qz.com/1039381/amazon-owns-a-whole-collection-of-sec...
Who isn't aware of it though? Every major retailer has their own store brand, and it's been like that since before any of us were born.
At least Amazon clearly marks their brand, unlike some companies create brands like "Open Nature" which is clearly meant to disguise their origin.