In my case I wondered the same thing.
I have one customer, a seed cleaning plant and often their shafts are bent. and then the grease gets a workout til the housing wears. The other thing that happens is the bearing sizes and then rotates in the flange, and it is run that way til end of season. I grow garlic commercially and just finished building a garlic cleaner, using PA flanges, and in this case, it will prevent rust between bearing and flange so I can replace the bearing without a fight.