Well for one thing, people seem to really enjoy victim blaming. It's much easier to say, 'The people who got infected have only themselves to blame, they were using an old an unsupported OS!' rather than to accept that maybe it's not necessarily anyone's direct fault if their computer got infected.
It was patched for 7 months before WCry started to spread. So it's not "The people who got infected have only themselves to blame, they were using an old an unsupported OS!" it's "The people who got infected have only themselves to blame, they were using an old and extended support OS and turning off Windows Update!"
