Copyrightable intellectual property is required by the Berne Convention to be for at least the life of the author plus 50 years. But US law provides much longer protection than that. Corporate "citizens" such as Disney continue lobbying for further increases, because they have a vested interest in making money from their properties as long as possible. So, copyrights have been extended many times over the years. The problem is that very little information gets into the public domain.
Life of the author plus 50 years is enough to take care of the author and his family, and that is really what copyright protection is all about. The corporations are not people and do not need such protection to be successful.