[jonsneyers]

The above claims are not very accurate.

JPEG and JPEG 2000 were based on the principle that the core codec was royalty-free but there might be patent-encumbered optional things (such as arithmetic coding, in the case of JPEG) that could be just left out if you want a royalty-free codec. Eventually it became clear that basically a de facto standard would always emerge that just skipped the patent encumbered things; JPEG XL doesn't have any (known) patent-encumbered ingredients for that reason: it's a bit pointless to add things to the spec that nobody will want to use anyway.

I don't think patents played a big role in the (lack of) adoption of JPEG 2000 and JPEG XR; more likely, in my opinion, the main problem was that good FOSS implementations were not readily available at the right time. The core codec of J2K has been royalty-free from the start, but it took quite a while before good FOSS software (like OpenJPEG) was available. Computational complexity was also an issue in its early days. For JPEG XR, even today there is no well-maintained FOSS implementation available; this is probably a bigger reason for its lack of popularity than potential patent issues. Compare for example with h264 (and x264), which had more substantial patent issues but nevertheless became very popular.

JPEG XT builds on JPEG, not JPEG 2000.

JPEG XS has a very specific niche use case (ultra-low latency, as a mezzanine codec for video production workflows), it doesn't have the goal of 'becoming popular' as a general-purpose codec.

JPEG is not MPEG. While both are working groups of ISO, which does have a policy that is not exactly "avoid the patent mess" but rather "don't talk about IP", there is quite a big difference in membership composition and attitudes between those two groups. Having a royalty-free baseline codec (and more recently, having just a completely royalty-free codec) has been something JPEG has been pursuing since the beginning (1980s), while in MPEG they're only recently coming to that conclusion (with EVC, no doubt due to pressure from initiatives like AOM).