There's a reason why JPEG and PNG are so popular: because they ARE stable and unchanging, in a world of failed adoption for APNG, WebP, HVEC, JPEG 2000, JPEG XL, AVIF, etc.

For image formats, broad compatibility is way way way more important than small gains in codec performance and filesize.

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Edit: From memory, this is something we learned the hard way back in the 90s and early 2000s, when image (and other) formats saw very rapid development and bandwidth was still hard to get. PNG was a huge improvement over GIF, and that mattered a lot over 56k modems. But the road to its adoption was very difficult, with many features only partially supported for years in different apps.

When WebP launched, it was objectively better in most ways compared to both PNG and JPEG, but it still saw limited uptake. Part of that was the titans fighting amongst themselves (other tech companies didn't want to adopt a Google format), but also by that point both JPEG and PNG were good enough and connections & CPUs were good enough. The incremental improvement it offered rarely justified it sometimes not working for some users on some browsers.

It's a similar situation for many other formats: H.264 in a MP4 is good enough, MP3s are still good enough, etc. On the other hand, PDFs and DOC/DOCX have different features depending on what reader you use (such as PDF forms, JS validation, accessibility, or DOCX not rendering the same on different readers), and it's a mess.