It's different. WebP was only Google's project. Even Mozilla haven't support it, heh. Nor Microsoft...
While AV1 is supported/promoted by many big players
http://aomedia.org/about-us/
WebP is barely better than JPEG (~15-20%) while AV1, HEVC or Daala are considerably better than that.
Also JPEG is damn good image format. There is still no other image format with 2x better compression than JPEG.
While H.264 and HEVC already outperform MPEG-2 by more than 2x on wide range of bitrates.