I have a small coffee farm, and I occasionally employ someone to pick the coffee. At commodity prices, it is hardly even economically sustainable to pick the coffee from the plant, much less get someone to pick up the ones that fall on the ground.
I personally, after 3 years of 'practice', can earn about 50 cents an hour picking coffee beans, probably up to double with a really good harvest. But of course even at 1 dollar an hour I am losing money by not doing almost literally anything else. More experienced coffee pickers in good harvests can earn 20 to 25 dollars a day picking coffee, and they are definitely not slowing down to pick any off the ground.
Each different fruit would have to be analyzed, but if industry standard is to drop it and leave it, its probably not viable to pick it up.
Value added products can also change the calculation. Instead of selling our beans as a commodity product, we process and roast them, yielding a higher value product. When I was a kid, my father and I collected fallen apples from trees in the suburbs to make applesauce with. It was worth it in that case to pick up that fallen fruit, although no one had picked through it first, and because we cleaned and boiled the apples it didn't matter that they had been dropped on the ground.