JXL has clear advantages and saying you don't see them means you either didn't attempt to see them or willfully ignore them
PNG/JPEG have strong support (nearly everywhere). I think of them almost as the modern TIFF - relatively simple, and almost everything supports one or both of them (few to no issues).
JXL may eventually get there (that indeed seems to be its goal), but for now I wouldn't drop e.g. PNG or JPEG support in favor of JXL now.
And arguably, perhaps never drop support; its such a prevalent format, even if all software (prevalent or otherwise) supports the format in 10 years, there will be such a huge stockpile of JPEG/PNG that something will need to be used to read/convert.
TIFF is not simple at all. There is a joke that it stands for “Thousands of Incompatible File Formats”.
In the GIS world we have a Cloud Optimized Geo Tiff. It is almost a standard now. This better than go to another format like Jpeg2k or ECW.
Tiff is an extendable format. Bit I am not saying that it can be better than JpegXL. Just a curiosity.
Even if JXL is superior in every single way, it doesn't make sense to throw out a perfectly functional graphics package and design language for a marginal bump in capability.
For me now, its marginal.
For a past customer, not at all. That customer really cared about delivering image-heavy pages quickly. There was a fairly big difference in customer perception at a timing threshold.