Investors got the message: don't compete with Amazon. They can remain predatory longer than you can remain solvent.
Now, not everyone shared the antitrust establishment's confidence that Amazon couldn't create a durable monopoly with market power. In 2017, Lina Khan - then a third year law student - published "Amazon's Antitrust Paradox," a landmark paper arguing that Amazon had all the tools it needed to amass monopoly power: