You will likely find your answer here https://www.vandenhul.com/wp-content/uploads/2019/09/Phono_FAQ.pdf
As A.J. explains, many times it is due to the very fine wire from the magnet assembly/transducer to the pins sustaining fatigue-failure. The very fine wire is often not long enough and becomes brittle with use. When it fails there is no repair. The manufacturer just replaces it. At a price.