Isn't this exactly what animated WebP [1] is supposed to address?
You should be mad at Google, who invented a whole new format based on obsolete VP8, which is even less efficient than its VP8-based WebM precursor. And it's literally because they couldn't make their VP9-capable decoder work in <img>. Animated WebP is Chrome's tech debt.
webm webp doesn't work everywhere (or very many places at all), you can't copy paste files around, it's mostly just (some) browser based.