1) People still running 10.6.8 were unaffected

.
2) The last time anyone installed a Blizzard game, they were using bittorrent.
3) Bittorrent is literally the
only way you can get certain legal files, such as chess tablebases. They are way too large to be distributed in any other way. These tablebases are much, much larger than a blu-ray disc and the bandwidth costs would be insane.
4) Anyone who uses utorrent probably had their machine turned into a bitcoin miner without their knowledge. Plus utorrent looks like crap and is adware.
5) I'm one of those people who downloads Linux distros using his Mac. Yes, we do exist, and if you're interested in Linux you tend to try out a lot of different distros which means a lot of bittorrenting.
6) This is a classic case of hackers going after the low-hanging fruit, targeting the weakest point in the security chain, which in this and many cases was the developer's website, not their software. They turned the developer's website into a distribution channel for a trojan, and took advantage of the open-source nature of the software to produce a trojan that looked legitimate and would work normally for a few days before unleashing the malware. If you want to get mad at anything, get mad at insecure websites.
7) This only happens because people actually pay the ransom. If you want this sort of thing to stop, have proper offline backups and never negotiate with terrorists of any variety.