I know you created a throwaway to troll, but I'll humor you anyway. I could come up with endless reasons why a company would want to require moderation, but at the end of the day: because they say so. Amazon created the platform, Amazon creates the rules.
I find it mind numbing that the same people that want to live on Parler because "freedom" simultaneously think a private company shouldn't have the freedom to choose who they do or don't want as a customer. Meanwhile gay people can't buy a wedding cake and that's A-OK because freedom.