Taxes are a factor, but a small factor. The larger factor is the internal logic of capitalism that treats labor as an input cost and profits as a residual. This is not a bad thing as it has enabled Amazon to deliver value to consumers better than any of its competitors, but it does impose those cost savings on the most vulnerable in capitalist societies, i.e., those without bargaining power.

But the solution is never to destroy Amazon and capitalist logic by artificially raising costs through labor cartels. Rather we should design policies to encourage Amazon and other corps to shares the risks and returns of success, and for citizens to take on and manage that risk. If I worked for Amazon, I want equity participation and rewards that come with the risks. Why should Bezos collect it all? It’s fundamentally immoral according to capitalist morality as espoused by Smith and many other economic philosophers. He who takes the risk, gets the reward (or the loss).
Bezos also has benefitted greatly from winner-take-all network dynamics.