Webkit was likely "saved" by the original KHTML license being GPL. At the time, Apple were wise enough (or desperate enough) to figure that they could work with such a license, although they were eventually careful to chisel out anything they could into BSD-licensed modules. And still they had to be dragged into the light more or less kicking and screaming (e.g. they had no public VSC until KDE people kicked up a stink in the press, and were just throwing huge swaths of code "over the fence" like they still do with XNU).

Indeed. Git repo at https://github.com/apple/darwin-xnu.

Note that that is 2 years behind. You can get a newer source dump from https://opensource.apple.com/source/xnu/xnu-6153.141.1/.

So, open source, but development isn’t done in the open. You can’t really expect you’ll be able to see recent commit messages or even just regular source dumps.