1. Mozilla is the only browser that has no legal way to provide integrated H.264. Every other major browser is backed by a corporation and can afford the MPEG LA fee.
2. While Google probably would prefer VP8/VP9 becoming the WebRTC standard, its not like they can't do H.264. So they have been dropping the ball on pushing people towards WebM and away from H.264.
3. (Speculation) Cisco probably made an exploding offer - "We can enable legal H.264 for all your users and foot the bill for it, but only if you agree to it before the WebRTC meeting".
4. No matter what codec wins at the WebRTC meeting, H.264 content ain't going away anytime soon. Mozilla has to have it either way.
This is an interesting maneuver by the H.264 lobby. It leaves Mozilla very little wriggle room. In hindsight, I have to wonder if a better deal could have been worked out by Mozilla actively seeking a license from MPEG LA for some fixed one-time sum in perpetuity in return for Mozillas' compromise on H.264. Maybe a kickstarter could have been then done to raise the required one-time fee. Who knows - maybe Redhat, Ubuntu etc could have been asked to chip in.
Sigh. Big money tends to get its way. :(