I think this might sound like a weird thing to say, but technical superiority isn't enough to make a convincing argument for adoption. There are plenty of things that are undeniably superior but yet the case for adoption is weak, mostly because (but not solely because) it would be difficult to adopt.

As an example, the French Republican Calendar (and the reformed calendar with 13 months) are both evidently superior to the Gregorian Calendar in terms of regularity but there is no case to argue for their adoption when the Gregorian calendar works well enough.

Another example—metric time. Also proposed as part of the metric system around the same time as it was just gaining ground, 100 seconds in a minute and 100 minutes in an hour definitely makes more sense than 60, but it would be ridiculous to say that we should devote resources into switching to it.

Final example—arithmetic in a dozenal (base-twelve) system is undeniably better than in decimal, but it would definitely not be worth the hassle to switch.

For similar reasons, I don't find the case for JPEG XL compelling. Yes, it's better in every metric, but when the difference comes down to a measly one or two megabytes compared to PNG and WEBP, most people really just don't care enough. That isn't to say that I think it's worthless, and I do think there are valid use cases, but I doubt it will unseat PNG on the Internet.