Think of labor as a resource like food, coal, iron, etc. A country only has so much labor power just as it only has so much of it’s natural resources. When it comes to building a country as efficiently as possible in which the most people are benefitted would you rather have foreigners take your limited natural resources for a payment that while helpful makes you eventually dependent on them or would you rather use that resource to build an economy with solid foundation based on local industry?
The thing about proper compensation under capitalism is that it doesn’t exist. A person is paid enough to cover their cost of living and the rest of the value their labor produces is owned by their employer. So even within capitalism that labor value is is more secure if it is kept within ones own borders.
This isn’t a perfect explanation I don’t think but I hope you get what I mean