I think there's more to this than Amazon being annoyed at the stupid taxes raised on imported goods. Same with price labels on items with and excluding tax; people just like the lower numbers better, and stores that don't show low numbers will lose customers even if they operate at the same price point.

Studies have shown that consumers will gladly visit restaurants that don't include tips in their prices over restaurants that do, even when the prices are exactly the same.

In a country used to not seeing the total price on store goods, hiding the tariffs away as a "+145% tariff" label makes perfect sense. Just raising the total cost and hiding the tariff, what the American governments probably would prefer, would put Amazon at a disadvantage against other stores that do show the split.

On another note, Apple got very upset at Facebook when they tried to pull the same trick regarding the 30% Apple tax. In that case, Apple forbade Facebook from making it explicit how much of the transaction was a tariff raised by an external party. Same trick, but different outcome (because Apple can force Facebook's hand).