I support the Chrome team with this one...

Something like an image format should either be widely used (ie. At least 5% of websites use it), or it shouldn't exist.

A format existing has a maintenance cost, a security cost, an extra barrier to people designing new browser's or web technology, etc. If fewer than 5% of sites use it, and all features can be achieved another way, then it simply isn't worth keeping support.

Sorry JPEG XL... You were a nice design, but ultimately you weren't popular enough. A bit like Server Push (web server can send your client data you'll need ahead of time saving a round trip), ScriptProcessorNode (JavaScript can mix/make audio realtime) and DANE (security with no certificate authority)... All cool tech that didn't manage to find a userbase.

How exactly are you supposed to use a format that isn't supported?

How would 5% of sites ever get to use JXL if it isn't supported in web browsers?

Here's one: https://github.com/niutech/jxl.js

Demo: https://niutech.github.io/jxl.js/

Libjxl's own WASM build: https://github.com/libjxl/libjxl/tree/main/tools/wasm_demo