LibGen already has "torrent per 1000 files" for a long time, some books also have their individual torrents but it's not common. I'm not sure why, but I think the problem is that files on BitTorrent cannot be directly addressed by hashes, it had to go through an intermediate step called a "torrent", which does not uniquely identify individual files directly. You can always select the one file you need from a huge torrent, but it's not as convenient as directly addressing files by their hashes.