The stylus of a phono cartridge is a consumable item, in other words it wears out with use, and can also easily become accidentally damaged, as it is extremely fragile.
As 90% of the value of a phono cartridge is in the stylus, it is often just as easy to replace the entire cartridge rather than just the stylus - this also allows you to upgrade to a better sounding cartridge to give you more enjoyment from your vinyl.