I imagine there's some amount of frustration on the part of people being told they should spend time implementing WebP, when APNG was a real working alternative

I imagine there's some amount of frustration on the part of people being told they should spend time implementing WebP, when APNG was a real working alternative circa ~2004 and nobody else was willing to implement it. (Admittedly, WebP does things APNG isn't capable of.) Reminds me of MNG, where we had an animation format with support for alpha and either PNG or JPEG style compression of frames, but it never got a pervasive browser implementation so it died. (I get the impression there were strong technical reasons for that, of course.) Coincidentally, MNG also indirectly solved this problem. JNG was a subset-format of MNG that provided JPEG-compressed static images with optional support for alpha, so implementing MNG implied implementing JNG. But we never got it on the web. At the very least, instead of just saying 'WebP is bad', they're putting their money where their mouth is and advancing the state-of-the-art in JPEG encoding so that people won't need WebP (other than the alpha channel use case, that is.)