“Huge profit increase even after the costs of shipping.”
Having Most Favored Nation status means the Chi-coms don’t pay for the shipping. WE pay the shipping through subsidies and grants.
Since the Chi-coms are World Trade Organization members, since 2001, it would take a lot to strip them of their MFN status.
It could be done but it would take a Trump with eight years ahead in the White House to do it.
That's why Amazon is flooded with Chinese suppliers selling directly into the US these days.
I recommend the Cultivate browser plug-in for Chrome and Brave - it's free and displays a little message telling you where the Amazon seller and the brand come from, making it easy to avoid Chinese products if you want to. Of course, in quite a few categories there is no competition - it's buy China or do without.