It's actually not Safari but WebKit. Gnome browser uses it as well (and a few others). I guess that makes it harder to sue? Since it's not a project that "belongs" to them?
Last time I checked (maybe 2015 or something like that?), Apples contributors are about 50% of the total contributors to webkit. I used to have a script to aggregate the data, but doesn't work now and I have no time to fix it. Maybe someone else wanna give it a try? The list itself is here: https://webkit.org/team/ / https://trac.webkit.org/browser/trunk/Tools/Scripts/webkitpy...