My assumption is these bot accounts are used for selling Likes/Follows on Facebook, and they Like everything in sight so that the paid Likes blend in.

That said, its unbelievably frustrating if you are trying to run Facebook ads. Nothing against foreigners, but I have to pay for every Like/click, and I'm sure they don't want to buy the local service I'm selling (and are clearly not reading the ad).

Its the ad exchange's job to curtail this sort of thing, and Facebook does a very poor job of it compared to e.g., Google. I hope they get it under control.