The US isn't really alone in this; allowing foreign entities to own a controlling interest in a domestic airline is not super common outside of the EU (where the "foreign"-ness of a company headquartered in another EU member state is kind of blurry anyway).

See, for example, Etihad's 49% stake in Alitalia, Delta's 49% stake in Virgin Atlantic, etc. -- significant investment happens, but controlling share is a lot less frequent.