Why do we have non-American companies in our defense?
Because we don't make stuff here any more, we out source the R&D/design work and we import the finish/manurfactured product.
Probably for the very same reason that no shortage of US defense firms are knee-deep in procurement for military weapons/programs in many other nations worldwide (such as S. Korea, Japan, Saudi Arabia, Qatar, Thailand, you name it). Land, Sea, Air and Space.
Believe it or not, I have heard BAE is a good company. Compare that to companies that are sending and selling our technology to China.