Earlier quoted context omitted.
Your assumption is that Amazon, the middleman, must exist. If Best Buy, a brick and mortar, were anything like Amazon, they would be under investigation as well. Nonsense comparison.
The GP made no such assumption
I might agree with you if this sentence used a generic term instead of "Amazon". However it specifically refers to Amazon.
I think people forget that Amazon did not operate as a middleman when they first appeared in the early 1990's.
Amazon was originally a bookseller, not a middleman for other sellers.
Not only does the sentence above from GP assume the existence of Amazon, it assumes that Amazon must act as a middleman for other sellers.