If you fish on brackish and saltwater, detritus will accumulate easily in both ends of the worm shaft. And the bushing will allow it to wear the shaft ends, even more so in cheaper ones. But I agree, decent bushing can mitigate or avoid this problem. But seems like decent bushes are pricier than cheap bearings...
Bushing allow to detritus get stuck between them and the shaft, in a way bearings don't do it.