Phoenix had an article on why Google decided to remove JPEG-XL.
https://www.phoronix.com/news/Chrome-Dropping-JPEG-XL-Reason...
The official justification seems to be a) experimental nature of JPEG-XL, b) lack of demand, c) maintenance burden.
Take it with a grain of salt. Personally I don't buy it.
I wonder what exactly they mean by this because JPEG-XL is a ISO standard. So if it's already standardized, how the heck is still "experimental" ?
Other than that there is nothing experimental in JPEG XL.
I see there's some confusion. A specification might be formalized in an international standard, but implementations of said standard can and often are experimental.
You don't magically turn code production-ready by having a committee sign off on a document.
So were JPEG-XR and MJPEG2000.