Chromium had it behind a flag for a while, but if there were security or serious enough performance concerns then it would make sense to remove it and wait for the jpeg-xl encoder/decoder situation to change.
Adobe announced they were supporting it (in Camera Raw), that’s when the Chrome team announced they were removing it (due to a “lack of industry interest”)
I have never understood why you can delegate a subdomain but not the root domain, I doubt it was a technical issue because they added support for it recently via
SVCB
records (But maybe technical concerns were actually fixed in the decades since)