Countries don't but governments and politicians very much do. "It's required from us by the EU" is already a common excuse, this is yet another treaty that will be used that way -- it solidifies the current copyright regime making it more difficult to introduce changes later.

This is the part I was referring to:

   In a nutshell, it gives each signatory authority to 
   create laws that satisfy ACTA's requirements. Without 
   getting into the issue of monism and dualism 
   (international legal concepts for how treaties embed 
   themselves into domestic law) it simply means that until 
   signatory states create enforcing legislation, ACTA does 
   nothing.
   
   An example would be that, once passed, a US federal act 
   that enforces ACTA is immune from challenges over states 
   rights (though not bill of rights challenges). To be 
   frank this isn't too controversial, there is nothing in 
   ACTA that doesn't satisfy the inter-state commerce 
   clause anyway.
   
   So undersand that ACTA isn't really the issue. What 
   people need to be prepared for is how states implement 
   it, which is where scope for abuse is.