After considering the nature of the electrical contact (the dangler touches only a few parts, which in turn contact a few more parts, which in turn contact some more parts, etc.) it's clear that the contact "area" can be rather small at times while parts are tumbling. It's logical then to run as little current as possible so as to preclude any overload at the contact points.
And checking in at commercial plating operations bears this out: barrel plating tends to be done at lower current densities. ie, as low as you can go and still get good plating.