Microsoft Edge implements ORTC. The problem is, the IETF RTCWEB working group was/is dominated by players from the SIP world who wanted to re-use their existing code. The argument was that WEBRTC devs would never need to touch the SDP, and all specification work done for SDP would have to be repeated for any other approach.

Of course, today's WEBRTC SDP, RTP, and RTCP is quite incompatible to existing SIP platforms (which usually dont support trickle ICE, RTP/RTCP bundling etc).