While i sort of know why, I’m not really knowledgeable enough to explain in a clear way, this article is pretty good. http://www.theregister.co.uk/2003/10/06/linux_vs_windows_viruses/ though old, it covers basics.
Its harder to trick someone to introduce malware to a linux system. And viruses need to propogate to be successful, the simple truth of numbers means to do this, you target the most prevelent, and easy to infect OS system, which is , you’ve guessed it…
AV for linux does exist, Avast being the most familar…
The advantage of AV for linux is a gives you safe way of checking removeable drives exposed to external windows systems, windows virus CANNOT infect linux, but linux AV can detect and sort windows virus on flash cards etc.
Now, Bourbon cream and a double espresso please cougar if you’re buying (i got them last time).