There's a thing called favspam, and has been going on on twitter for at least half a year now. Seems to be on other social networks too.
These guys use a bot or service, that fav everything of a subject hashtag. The frequency of their fav is like 1 per minute.
Favspam works, because it get people to know and read about them, and after you got fav a few times, you are pleased and often you follow them. These accounts otherwise looks normal real person accounts.
Typically, they follow very few, like below a hundred, but has thousands of followers, and their fav count is in hundreds of thousands.