Whatever are you referring to? JPEG XL had already been merged into Chromium, prior to being removed again (without a proper reason ever given). As far as I know, the JPEG XL developers have offered to do whatever work was necessary for Chromium specifically, but were never taken up on the offer.
Same thing with Firefox, which has had basic support merged into Nightly, and a couple more patches gathering dust due to lack of involvement from the side of Firefox. Mozilla has since decided to take a neutral stance on JPEG XL, seemingly without doing any kind of proper evaluation. Many other programs (like GIMP, Krita, Safari, Affinity, darktable) already support JPEG XL.
People are not getting upset because projects don’t invest their resources into supporting JPEG XL. People are getting upset because Google (most notably), which has a decisive say in format interoperability, is flat out refusing to give JPEG XL a fair consideration. If they came up with a list of fair conditions JPEG XL has to meet to earn their support, people could work towards that goal, and if JPEG XL failed to meet them, people would easily come to terms with it. Instead, Google has chosen to apply double standards, present vague requirements, and refuse to elaborate. If anyone is ‘preventing even foundational elements of a successful effort’, it’s Google, or more specifically, the part that’s responsible for Chromium.