Hard disk and bandwidth of jpegs are almost certainly negligible in the era of streaming video. The biggest selling point is probably client side latency from downloading the file.

We barely even have movement to webp &avif, if this was a critical issue i would expect a lot more movement on that front since it already exists. From what i understand avif gives better compression (except for lossless) and has better decoding speed than jxl anyways.

> We barely even have movement to webp &avif

If you look at CDNs, WebP and AVIF are very popular.

> From what i understand avif gives better compression (except for lossless) and has better decoding speed than jxl anyways.

AVIF is better at low to medium quality, and JXL is better at medium to high quality. JXL decoding speed is pretty much constant regardless of how you vary the quality parameter, but AVIF gets faster and faster to decode as you reduce the quality; it's only faster to decode than JXL for low quality images. And about half of all JPEG images on the web are high quality.

The Chrome team really dislikes the concept of high quality images on the web for some reason though, that's why they only push formats that are optimized for low quality. WebP beats JPEG at low quality, but is literally incapable of very high quality[1] and is worse than JPEG at high quality. AVIF is really good at low quality but fails to be much of an improvement at high quality. For high resolution in combination with high quality, AVIF even manages to be worse than JPEG.

[1] Except for the lossless mode which was developed by Jyrki at Google Zurich in response to Mozilla's demand that any new web image format should have good lossless support.

jxl let’s you further compress existing JPEG files without additional artifacting, which is significant given how many jpeg files already exist.