It's not a matter of economics, corporate policy or belief in people -- it's a strategic matter. A country needs a secure and stable pipeline for personnel as much as for any other strategic asset.
A country also needs to keep up and learn from other countries. That means working with and integrating technologies, ideas and, yes, personnel from other countries.
It's a balance thing and Anduril has a hard job in trying to strike the balance, but they have to do it. The defense industry is not simply a number-goes-up operation.