> Do you harvest apples by bulldozing the orchard and sifting out the fruit?

Isn't this how we harvest cranberries?

> don't really understand why nodule gathering isn't already done - just with some kind of robotic fingers or aimed suction devices

The nodules may facilitate some weird deep-sea electrolysis that lets these ecosystems respire. Removing the nodules delicately is better than dredging. But it may still be a death sentence.