[brigade]

WebP was I believe the first image format that supported lossy compression with transparency. You could argue that you can just use PNG if you want transparency, but allowing lossy compression if you need alpha is more like 10x smaller, not a mere 60%. Also it came out back in the era when 4MB for a web page was a lot.

AVIF was the first format accepted by the web that supports HDR (not already tone-mapped HDR, true HDR.) Which maybe you don't personally care about, but is something that fundamentally cannot be done with existing JPEG and PNG implementations.

AVIF might not have happened, and the above paragraph might have read "HEIC", if HEVC had had similar licensing terms as H.264. But there's no predicting that stuff before it happens.