The adjuster cables are tensioned every time the hand brake goes on and off. It is the handbrake use that wears them out.
I figured that frequency of use was the most likely reason, but it seems counter intuitive that the self adjuster cables would wear out and break much faster than the shoes wear out. I just replaced adjuster cables on two TCMs whos brake shoes were not even close to worn out today.
there are at least 2 good reasons.
the first is the same reason starters (and ring-gears) are replaced in forklifts so much more often than in cars, trucks and ag-equip. In a car you start the car an average of 3 times a day, in a forklift you may start the motor an average of 6 times a shift or more. In a car you may not even use the park brake, while in that forklift the park brake may be used 6 times an hour.
The other is the tendency to run over strapping and stretch wrap, that winds itself around the wheels and brake parts, causing all sort of problems
It is simple, forklift brakes are more or less in constant use.