Pirated content is free content: you can't really say that one person pirating your game equals one lost sale. Would have he bought it, if he was given no alternative choice to get it? When the price is null, there are low to no expectations as to how good the product should be, hence there's a lot more people using it. Someone gives you something that has value for free in the street, would you take it? There's a good chance the answer is yes, even if you do need it.