What benefit could a 3rd party conceivably get out of faking clicks on Facebook ads? Is there a rev share at all with publishers, like with adsense?
A lot of people also have bots to see who/what is advertising on FB to see what is working, what ad text people are trying, etc. Mostly aff marketers trying to stay ahead of the game. There are also SaaS companies scraping ads and landing pages and selling that data.
I'm sure there are other reasons as well...