The problem is that old PNG and JPEG are good enough for most purposes. They are certainly not as efficient but with todays technology and bandwidth, there is little downside to using JPEG and you know it will be supported everywhere.
It is not the case for video. Video is still a huge bandwidth hog, and finding better codecs is worth it, that's why they get better support. Webp is a clever hack as it is essentially a single frame webm video, so if you have webm support, which is worth it, then you can have webp almost for free, JPEG-XL doesn't have that incentive.
It is not the case for video. Video is still a huge bandwidth hog, and finding better codecs is worth it, that's why they get better support. Webp is a clever hack as it is essentially a single frame webm video, so if you have webm support, which is worth it, then you can have webp almost for free, JPEG-XL doesn't have that incentive.