Help with Problem "Rental Service" from 2018 Jan. Silver section

In the solution, there’s this line: “Secondly, we want to rent cows that produce less milk over cows that produce more milk.”. I don’t understand why this would be true. What if the price for a cow that produces less milk is way higher than the price for a cow that produces more milk? I am probably missing something here. Thanks in advance!

How would this happen?