That isn't a good justification for calling JPEG "archival". HEVC outperforms h.264 just as BPG outperforms JPEG but like HEVC, support for BPG is still extremely limited and adoption is ultimately what determines whether something can be discounted as "archival".

Sure there are JS polyfills but those aren't going to work well on mobile devices and until content creation tools like Photoshop and desktop operating systems like Windows and Mac support exporting and reading BPG, it's unlikely to see much adoption.

Archival as in has to support decades of old images. It's not a format that's being heavily modified or is going to see any hard transitions in coding/decoding.

FLIF and BPG are development formats and where you look towards the future, not the past.

JPEG is the main format in which images are produced and distributed these days. Even cameras that produce "RAW" natively will usually have their output converted to JPEG for distribution.

No one disagrees with you. But for that very reason it's locked in supporting those old files. I.e. archival.

JPEG isn't going to morph into some brand new format that supports arithmetic coding. New formats will adopt those, specifically because they don't have to support decades and petabytes of files.

Not to mention, if you've ever actual written a JPEG decoder/encoder; the format is not conducive to coding outside of it's HUFFMAN/quantization format. PNG can add those things since it's actually an extensible format, but even then...why? It's not like the libpng everyone has installed will magically support them.

Isn't BPG lightyears ahead of FLIF?

Only for lossy. Lossless is FLIF's main game.