I'm active in many art communities on the web for whom being able to view and share lossless images are table stakes. Also many other communities for which being able to view and share lossless screen captures is fundamental.
I can accept a claim that JPEG-XL is not the best format for it, or that it is good, but not worth the complexity and extra surface area it introduces. I can not accept a claim that "lossless just isn't very useful on the web".
What percentage of the web is that 0.1% ? 0.01% ?
I think its correct to say a use case that is very niche on the web isn't super important to the web. Especially when there already exists a bunch of lossless formats. After all, the value proposition of jxl is to save some bytes. It would be different if the point was introducing images as a whole.