Possibly other advertisers trying to push competitors away from facebook so BigDickPillz Inc can have it all to themselves?
The game is as jiggy said. Force competing ad buyers to pay for what appears to be non-productive traffic by forcing ad clicks. Since the real views are dominated by false views, the conversion rate on whatever is being sold appears to be horrible. The competitor goes elsewhere, and the scammer maintains access to artificially cheap ad inventory, since there are fewer bidders.
It's a well known problem. Considering AdWords is Google's primary source of revenue, they work hard at it. For a tiny bit more directly from Google, see: http://support.google.com/adwords/bin/answer.py?hl=en&an...
By far the most likely explanation in my opinion. Even if it's not the correct one, some of the traffic is almost certainly these kinds of bots.