Here's a summary of the main points: https://jpegxl.info/why-jxl.html https://jpegxl.info/why-jxl.html Basically lossy WebP and AVIF are video codecs, which a

Here's a summary of the main points: https://jpegxl.info/why-jxl.html https://jpegxl.info/why-jxl.html Basically lossy WebP and AVIF are video codecs, which are designed for the kind of quality you want when you can only see an image for 40 milliseconds or less. For still images, higher fidelity is usually desired but the video codecs tend to struggle to even keep up with the old JPEG at those operating points. Similarly, video codecs are not designed for progressive decoding (rendering previews of a frame based on partial data), because that's a feature that doesn't make much sense for video. For still images on the web, progressive decoding is considered a desirable feature though to improve the user experience.