"Hey, this trojan has stolen our CC numbers, photos and personal documents, but at least it's not a virus! THAT would have been really bad...".
And please try to keep up with the latest developments, this trojan requires no user intervention. Not running Little Snitch + antivirus at this point is just ignorant and asking for it.
I think that's more to do with "herd immunity" than anything else. There haven't been enough macs communicating with macs to have widespread damage from a mac virus.
Note a Trojan, is not the same thing as a virus. A virus self propagates, a trojan propagates when a user overrides a security warning.
Viruses have been a problem for Windows for decades, but not a problem on macs, since the late 1980s, possibly early 1990s.