Money may still be made from it, but that doesn't mean they were originally created with the idea that today they'd be making money this way. Most of the money is generally made within the first couple of years after release.

My preference for copyright would be 30 years or until death of the author, whichever is longer. If there's no living author or the rights have been transferred, then it's simply 30 years. This gives plenty of time to make money from it, it means the author never loses control over their own thing during their lifetime, and their family can benefit from it if the author dies shortly after publication.

More than this is just corporations milking creations from the past.