A tree root may easily be the problem as could galls. I've been rather surprised recently finding galls on roses which had never suffered trauma, quite a few of which have always been grown in pots. You would be quite surprised how parts of a bed can deteriorate while the rest of it remain productive. The tree root issue can help cause that. I doubt they are at their "normal expiration date". My youngest sister has three Queen Elizabeth bushes, planted by the original owner of her house in 1966 when it was built. She bought the house from the original owners. These bushes are HUGE. I've pruned them by half, leaving them easily four to five feet tall, only to have them explode back up to nearly ten feet. Those things are nearly fifty years old and are still going strong. There is a Queen Elizabeth here which is as vigorous and has been neglected, even tortured because of its situation, since 1975 when this house was bought.
My first suspicion would be a variety which just isn't terribly vigorous to begin with. The second would be a soil issue. The third would be buried bud union or gall. A virus, or multiple viruses, is a very good possibility. They were only beginning to do anything about viruses thirty years ago, and not every producer. It's been estimated that by the 1970s and 80s, a full 80+% of the American rose crop was infected by at least RMV.
