It's more likely related to security, image formats are a huge attack surface for browsers and they are hard to remove once added. JPEG XL was written in C++ i

It's more likely related to security, image formats are a huge attack surface for browsers and they are hard to remove once added. JPEG XL was written in C++ in a completely different part of Google without any of the safe vanity wuffs style code, and the Chrome team probably had its share of trouble with half baked compression formats (webp)