We've been here before. Jpeg and PNG are "good enough" and consumers aren't going to get behind anything that is slightly less convenient.

Tell that to all the users with iPhones chucking out HEIC/HEIF images by default, which are much less convenient

I'm under the impression that one of the main selling points of JPEG XL is that it's backwards-compatible, so once everyone has a decoder implementation, every existing JPEG comes along for free without anyone having to reencode any old photos. I suspect consumers wouldn't notice the difference if devices started emitting them, and in the meantime that means there's no harm in continuing to emit classic JPEG for as long as you want.