I think you are misinterpreting section 6. Section 6 is about the requirements for software that use the library. Specifically section 6 is about software tha

I think you are misinterpreting section 6. Section 6 is about the requirements for software that use the library. Specifically section 6 is about software that statically links to the library (section 5 is about dynamic linking). If you statically link to the library, the resulting binary contains the library and you are required to provide object files so that a user can relink with a different (and hopefully compatible) version of the library. In the case of Apple, they have made modifications to the library itself. They are then using the library, with modification, in Safari. Safari can be released under any license as outlined in section 5/6 but not the modifications. Those need to be released.