How can studio wiring just suddenly go bad?

Was in the studio last night working on some after hours recording and suddenly both my audio monitors started buzzing...like a grounding problem.
So after two hours of methodically diagnosing I isolated it to the reference speaker cables. The old cables were custom built cables that we installed in 1992. They've been through a couple of moves since then but were working fine up to last night. Today am changing both speaker cables out with new Mogami cables. But still wondering; how is it that stationary wiring just suddenly goes south? I understand something like a guitar cable malfunctioning due to constantly being coiled and uncoiled, etc...but stationary studio wiring? It's a mystery.

A little thing called oxidation. Over a period of time moisture in the air and particles settle into the braiding and set up shop. If you have 1/4" plugs, XLR or any connectors clean them with DeOxit. Then check the cable and see if it has been exposed to the air, hit that with the Deoxit. Or trim the ends and make new connections.

I work on friends computers at times when they go crazy and it's the same thing with them too. Just reseating all the cards inside and Deoxit most of the time does the trick.