IIRC the reason why SwiftUI isn’t a separate library is that it’s developed in lockstep with Swift, meaning that each release is dependent on new features in it

IIRC the reason why SwiftUI isn’t a separate library is that it’s developed in lockstep with Swift, meaning that each release is dependent on new features in its contemporary release of Swift. That’s a problem because they stopped building Swift into third party app packages a few years ago in effort to bring down app download sizes, but that means that apps have to deal with whatever version of Swift comes with the user’s system. The best middle ground would probably be to ship Swift as a periodically updated package.