The thing is Apple used to do this correctly. Back when they still shipped OpenSSL (albeit some ancient version), they had actually patched OpenSSL to do cert validation against the native keychain and only ever had Keychain as the source of truth. You can see this in https://github.com/apple-oss-distributions/OpenSSL098/blob/O...

And curl was patched to use the native TLS implementation (SecureTransport) which obviously used Keychain as well.

For some reason when they switched to LibreSSL everywhere they decided to ship their own copy? I don't know what they were thinking.