Piracy: ꜱᴀɪʟ ᴛʜᴇ ʜɪɢʜ ꜱᴇᴀꜱ

It is less likely, but viruses can absolutely come in non-executable file types. A quick look at VLC media player's changelogs show that there are a lot of updates to fix security issues. Same with PDF files and security issues in Adobe Reader (to relate to your ebook mention). Can't speak to music, but image files are also a common choice for malware embedding. For a good while the easiest way to run homebrew on PSP was by taking advantage of an oversight with how it handled image files to get it to run unsigned code, and similar exploits exist in image reading software.

The only thing someone spreading malware needs is an opportunity. It's not hard to imagine someone tracking torrents for things like cult classic films and then taking advantage when seeders dry up by uploading their own torrent and faking seeders (or sockpuppeting them by using botnet machines) to get their compromised torrent listed at the top of results for that search. I've lost track of how many times I was surprised to find something I thought was reasonably popular with only 15 seeders. It wouldn't take much to game those numbers.

Hell, it's probably even automatable with enough of a media library and time spent scripting. Theoretically could be a good way to build a botnet, or collect endpoints for a shady residential proxy service.

For the record, I've only had issues with TPB content when I was being unreasonably risky (in retrospect) and my antivirus caught things before I was truly infected.

That said my rambling point is: why take the risk when there's plenty of safer options even just in the public tracker space?