Probably-stupid question from a non-specialist: if you're digitising an existing real-world picture and want really high fidelity, then why would you convert it to a lossy format like JPEG?
Fair question. The image was assembled way back in 2014 or earlier from a large number of tiled JPEG source images, so the quality had already been compromised. Also, JPEGs are essentially viewable on any device this side of 1990 and way smaller than lossless formats. These days I would consider webp in preference to JPEG.
https://commons.wikimedia.org/wiki/File:Panorama_of_Sydney_f...
This is likely to become a more frequent issue in future.