Something to keep in mind is that governments in the US govern at the pleasure of the people so governed. "We the people", as it says in the Preamble of the US

Something to keep in mind is that governments in the US govern at the pleasure of the people so governed. "We the people", as it says in the Preamble of the US Constitution. So if the government has an interest in enforcing copyright, that's because the people (whether or not they are intellectual property holders themselves) told the government to enforce copyright.