Apple never fully owned WebKit in the first place - most certainly not back in 2003. There was an extremely public and messy divorce period with the KDE codebase[0], and to this day there's still KHTML/KJS-derived code in WebKit that has to be sublicensed under GPLv2 for redistribution purposes.
If we're going to split hairs over the whole "Blink is an inferior WebKit fork" brouhaha, we shouldn't forget who Apple sherlocked to get there. After all, turnabout is fair play.
Strategically it makes no sense to not own something that important.
Remember: Safari was created when Apple’s 5-year deal with Microsoft that made Internet Explorer the default browser for MacOS X expired in 2003.
10 years later. Google forked WebKit to create Chrome.