Why Fiber Timing Gears

[mshmodela]

A newbie question:

If?? I've read the many threads about fiber timing gears Ford used them from the start to finish of the Model A and the start of the flat head V8. Now clearly Ford did this for a reason if that's true. Might it be a mechincal safety? In the event something when way wrong with the engine that the timing gear would give way, preventing further damage? Think of a shear pin, on some tractors or jet engines, why not a "shear gear" if you will ?

Just wondering...