Zynga has strong lawyers. They would force small devs to take them to court, if they could afford the legal fees, then settle if they had a strong case. By then Zynga's game went viral and the smaller devs lost their first mover advantage. The SF chronicle wrote a great piece about these tactics a few years ago. The article showed how they cloned FarmVille, then settled with the victim for 11 million (FarmVille would make a billion in rev that year). im on mobile and can't search for the article rn