I think the source is zero sum thinking and shallowness of thought. Amazon is profitable while they are not therefore it is Amazon stealing from them. There is a logic there that could be circumstantially correct but is loaded with fallacies and self-serving thinking.

Naive economic intuition has proven shockingly bad - especially historically. It is one thing not to grok rate of returns or market direction or make poor investments. Those people would be geniuses compared to historic economic fallacies.

We are talking things like the Ancient greeks thinking wealth could only be earned by conquest (logically implying that someone who conquered the entire world and enslaved it would be very rich but would not grow wealthier) and medieval thinking that merchants had to be frauds to sustain themselves given that goods had a value the same everywhere - despite the fact travel was known to be slow risky and expensive meaning just being a transporter is clearly an honest service even with the fallacious universal value assumption. Even if you are a lord who can afford something you may not have the time to travel to exotic locales to buy it directly from the source.