Yeah, that is all odd to me; Google cited lack of "interest from the entire ecosystem" (https://bugs.chromium.org/p/chromium/issues/detail?id=117805...). Mozilla also had an experimental JXL implemenation out there. I'd hope, like you said, that the browser vendors had enough of a backchannel to keep a good thing from fizzling because each is uncertain if the others will implement it.

But if the Chrome folks did know they had all three major browser engines were ready to go, along with the positive noises from Facebook, Adobe, other parts of Google, and a few other notable folks, that seems like a solid base of support, unless you're really expecting the world to go all-in on a format before a browser supports it without a flag. So I guess I wonder if it's that the Chrome team had set the bar high, that they hadn't expected Apple to support JXL at the time they made the call, or something else.