Digital products have difficult issues of copyrights because of their "public good" properties

Digital products, like music, video games, are "non-rivalrous" and "non-excludable". These are the two properties that we use to refer to public goods. Digital products are "non-rivalrous, because due to the modern technology, we can almost have infinite copies of any digital product. Therefore, the marginal cost of production is infinitely close to zero. Digital products are "non-excludable", because once one consumes the product, one can always share with his friends or even everyone else by uploading to the Internet. Of course, such action is illegal, but it is too difficult to check every uploading. So it is reasonable to say that legal forces are hardly to protect the copyright of a single digital product without any services afterwards because of its public good properties. In conclusion, I think that it is never profitable for firms to earn money purely based on digital products but the services combined with the products.