I'm not related to the Safari or any other browser team in any way. But I totally believe that it's a giant amount of work. I personally researched the effort which would just be required to implement webrtc data channels in a server application and have been rapidly been put off after seeing that I would need to have support STUN, TURN, ICE, DTLS and DTCP. With each of them having giant specs. The media formats and all the JS APIs would add on top of that.

I guess it's also not an easy decision to "just include libwebrtc" into ones own application, since that's a giant dependency which pulls in lots of chromium code.