Safari team is really strange with their priorities, most of the time they are dead set on implementing specs last, but every once in a while they decide a feature is important and they implement it faster than everyone else. For example, backdrop-filter was supported in safari way back in 2015, while other browsers added it multiple years later.
I suspect it is the influence internally from other product teams. WebKit is used in so many places within MacOS and iOS, someone recently wrote a blog post looking at the CSS used by Apple, :has() and some other WebKit only css was heavily used.
