I don't know the answer to 1 or 3 because I'm not a FB insider, but I can answer #2 for you:
> 2) Where do these click/like farms come from, and what's in it for them?
All you have to do is go on Fiverr and see people advertising Facebook likes for $5. The bots like a bunch of other pages and posts to simulate "real human activity", then the sellers direct all the bots to "like" a page that their client paid them to like. Rinse and repeat.