Earlier quoted context omitted.
Because it’s a great idea but for instance the Linux kernel would have to come with documentation that mentions the tens of thousands of authors. A massive undertaking that doesn’t help anyone, really.
Something like https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin... ?
At least, I've seen the Copyright notice for the California Board of Regents in the macOS startup debugging.