Fruit picking is a large part of the farmers' cost. All the extra cost of transportatation, storage, wholesale logistics, retail and markup matters for the retail price, but that's not relevant - the farmer is competing for a tiny share of that retail price, and if that extra ten cents goes out of their share that easily makes it unprofitable.

Your example with milk is a very good illustration - something that raises the farmers costs by a few cents is much more important than what it might seem based on the fact that the difference is small compared t owhat the retail buyer pays.

All the leverage that farmers have can't get them more than 9 cents/liter. That's it, there's no hope for them to earn 18 cents/liter - sure, the wholesalers probably could, but why would they gift money to other businesses without any need to do so? So if your milk production process gets 1 cent/liter more expensive (but your competitors, possibly far away, are still willing to keep the same price), you can't get 10 cents/liter, it simply wrecks your profit margin - if your profit margin was 11% (1 cent/liter profit out of 9 cents/liter revenue), you might as well go out of business since you won't be earning anything.