It's a legal distinction. Laws say that they're different. Also there's a number of material differences that justify that different treatment. Theft removes

It's a legal distinction. Laws say that they're different. Also there's a number of material differences that justify that different treatment. Theft removes the object from someone. Copyright infringement does not. Theft (as tipified in my country, opposed to "hurto" or "apropiación indebida", sorry don't know how to translate those) means certain quantity, violence on persons or things. Even if the same laws were applied to digital content, there would be impossible to convict anybody without specific laws, because taking something from someone without violence, dameges and not depriving the owner would amount as a small fine, not worth the legal costs. There is a concept in penal law over here that's called "punibility". The idea is that certain behaviours can't be controlled using criminal law because it's impossible to keep an eye on everybody: "behaviour that's socially accepted". If you need a policeman on every citizen, that also needs to enter your home to see if you're acting bad... then it's a bad idea to criminalize. The punishment isn't uniformly applied so it's even more unjust.