Distributors suffer mechanical wear or electrical failures like shorts and loose wires. Parts can freeze up from rust or break from abuse. Oil, dirt and moisture can cause additional problems. There are some NOS (new old stock) distributors available for classic cars, but they are hard to find. Luckily, most distributors can be rebuilt, unless they are damaged or weathered beyond repair.
This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/Articles/2007/10/03/Distributor-Rebuilding-Tips-from-a-Pro