MPEG-LA did not claim to have all possible VP8 patents either.
Note that MPEG-LA is basically a group that sets up convenient one-stop licensing, there's no such thing as being a "member" per se. You can be part of any of their patent pools, or not, if you believe you have essential IP.
This is not the first time Nokia did this. IIRC, they also threatened Ogg when it was being proposed as the mandatory codec for the <video> element.
Certain companies that have large installed bases of H264 hardware certainly have a vested interested in seeing H264 as the mandatory WebRTC codec.
http://datatracker.ietf.org/doc/draft-dbenham-webrtc-videomt...
IETF's royalty-free commitment isn't as strong as W3C's so unlike the HTML5 codec were they were just filibustering alternatives, they are actually arguing for H.264 to be MTI. But the VP8 camp is strong enough to at least prevent that, even if not strong enough to prevail as MTI itself.
There's some overlap with the groups that didn't want Opus made MTI as well (one of them submitted a patent against it too).