Bpoletti is exactly right. The stylus is what wears out. On MM cartridges, the stylus is 95% of the total price of a new cartridge, and in some cases it’s actually cheaper to just buy a whole new cartridge if you shop around. Stylus profile has a lot to do with stylus lifespan, because of the size of the contact area. A conical / spherical profile will only be good for 300 hours, while a elliptical could go for 500, and a line contact 800 or 1000. Depending on how frequently you play records, you might need to replace the stylus because the bushings become dry and brittle from age before the stylus tip wears out.
