Green Grocer mystery solved

Every shopping center in OZ has the standard supermarket, but also - to my great delight - a bread bakery, butcher, fishmonger and a green grocer. But one thing always puzzles me about what I see in the "fruit & veg" shops--the size of the produce. Sweet potatoes are the size of small watermelon, celery half way to sequoia status, uber jumbo broadbeans, cucumbers doubling as jousting poles. I mean, what can be the advantage to growing green onions into the size of a bush when the green parts are now woody and unpleasant?

Discovered the answer this morning: farmers here are paid by weight, so there is great advantage and savings in effort to let the produce grow very large. I'm not sure of the benefit to the consumer. I wonder how all of this works in the States. If US/Canadian farmers are paid by weight (and I don't know) why do they harvest their crops at manageable sizes? Let's say that North American consumers demand vegetables at their optimum size---why not Aussies? Not all produce suffers from steroid-envy, thank goodness, because I really do like the green grocer experience.