Answer
The price reduction in order to increase quantity sold doesn't account only for the additional quantity produced, but for the total number produced.
Work Step by Step
If a monopoly decides to increase revenues by increasing production, then it needs to lower the price as well in order for the extra quantity to be sold. By decreasing the price, all the units are affected, not only the additional ones. So, the price reduction doesn't account only for the additional quantity produced, but for the total number produced.
