Because it is actually possible to lose manufacturing knowledge over time. Manufacturing things in your country now allows you to more easily manufacture different things in your country in the future. It's a lot harder to make things if your manufacturing talent is spread across multiple countries, especially so if you're making anything that cannot use already commoditized components.

The differences in economies and cultures on the international scale is a capitalism cheat code. We are morally and logically obligated to protect our citizens in all contexts. That doesn't mean "fuck everybody else". It only means prioritizing.