I don't think it's due to manufacturing costs. Just look at how much insulin costs to make and the price it's sold at in the US.

This is how companies think:

If you can make something in the US for $5 and sell it for $300 you make $295 profit.

If you can make it in China and ship it to the US for $4 you make $296 profit.

Therefore its better to make it in China. They disregard literally every other benefit.

What you give as an example is a product with insanely high margins. Here, it indeed makes sense to produce it in your home country, because it won't make a huge difference.

Most products on a market have slim margins and here such production costs make a huge difference in profit if the buyer is not willing to pay much more for products (partially) produced in the home country.

3M N95 masks are 1.9 dollars each, while the Chinese ones KN95 are 0.4 each, korea made kf94 masks are between 0.5 - 0.8. Unless 3M masks have some magic in itself (like make me immune to covid), the pricing doesn't seem very appetizing

I think it is pretty self explanatory.