Mozilla's position for some time now has been, "we aren't opposed to shipping JXL support, but we'd want to ship a decent implementation in a memory safe language, not the reference C++ implementation". That position hasn't been met with very much criticism.

Google's position, on the other hand, has been a flat-out "no, we will not ship JXL". That's what has been met with criticism. Not an imagined reluctance to shipping a C++ JXL implementation.