HEIC is basically an image format hacked from a video format. It is not optimized for still frames. In fact the largest resolution supported in the frame coding is 8k. While hidden from the user frames larger than 8k are coded as multiple frames in the same image and there can be artifacts at the frame boundaries.
As I understand kt JPG-XL is an image format through and through with support for high bit depth (higher than HEIC) and terapixel images.
The other thing is the reference encoder/decoder is royalty free, open source, and freely available. Presumably it would just need to be integrated into DXO…. Not saying it’s super easy… but much of the hard parts are done already.