I suspect "Linux ISOs" are not actual Linux .iso images but ~pirated~ movies, music, and digital books ;)
No way!
Joking aside, a few early commercial Linux distro (Red Hat, Yellow Dog, SuSe, Corel Linux) had really nice packaging and media artworks. I'd love to collect them.
Yes, seriously, my intro to linux as a kid was seeing the slick Red Hat boxed media on the shelves at CompUSA.
ding ding ding
Thrift stores will often sell used DVDs for $1. No piracy involved, no copyright issues as it's a physical disk which can be legally sold on.
The "questionable" piece is ripping the DVD to a home media library to play via Jellyfin. Which might be fair use in some countries.