Similar to lomcevaks (there is actually an entire family of these), multiple snap rolls at high speed can overstress the crankshaft. The higher stresses from gyroscopic maneuvers are mitigated with the lighter, composite props.

Of course, there is always the inverse relationship between (speed + g's) and fatigue life, too. High speed/high g entries will exponentially reduce the number of cycles before failure. That's why performers like Sean Tucker rebuild their airplanes after every air show season -- they simply cannot safely afford to allow high stress hours to accumulate on the airplane.

Rich