"copyright owned by the contributor" means that as the project matures there will be way too many contributors. To change the license for the project to somethi

"copyright owned by the contributor" means that as the project matures there will be way too many contributors. To change the license for the project to something that is not Apache-compatible Apple would have to ask every contributor to re-license their code, and if the code author disagrees re-implement corresponding parts. In practice that's a signal to every one that the licensing terms are very unlikely to ever change.