A recent story on NPR(!) exposed a fake news site set up by a progressive to troll the alt-right. http://www.npr.org/sections/alltechconsidered/2016/11/23/503146770/npr-finds-the-head-of-a-covert-fake-news-operation-in-the-suburbs
That article explained the real motivation for fake news: MONEY!
Fake news is nothing but click bait. Sites are trolling for page reads, so they can deliver ads at best, or malware at worst.
It’s no different from the blog pimping you see on FR.