That's completely true. Years ago I worked for BT Laboratories, and I often visited the test house where they tested undersea telephone cables, stretching them and bending them to see how they stood up to various kinds of mechanical stress. If an undersea cable breaks during service (for instance because somebody has dragged their ship's cable across it on the sea bed) then that is a pain because it is expensive and time-consuming to send out a cable ship to pick up the cable and repair it. And meanwhile, the cable owners are losing big money. Therefore the reliability of undersea cables is a big consideration.
So far as I remember, all the cables were designed for a 25 year service life. Nobody thought that a cable could be constructed that would last forever. And 25 years made perfect sense, because technological advances generally have meant that a cable is obsolete - due to being succeeded by newer, better cables with vastly greater traffic capacity - long before the 25 years are up. Therefore the fact that the cables don't last forever isn't a problem.
To some extent this approach carries over to space elevators. Presumably after a space elevator had been built, if the technologies involved continued to progress, then newer, better, faster, cheaper etc space elevators might be built while the old one was still in service. Eventually the original one could be made obsolete by the newer ones. Economically, nobody would care anymore if it stopped working.
However, the difference is in the safety aspect. When an obsolete submarine telephone cable stops working, it can simply be left where it is. However, an obsolete space elevator would have to be carefully and expensively dismantled otherwise it would continue to be a threat to the folk living below. Until then, it would be more like an obsolete nuclear power station than an obsolete cable in terms of risk management.
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