First, get rid of the idea that the factories have hundreds of lines running all the time, turning out every known caliber.
That is not true. Even the bigger ammo factories (military excepted) run a batch of one caliber. Then they change over a line and run a batch of another caliber. How long a line will run a given caliber depends on demand; and how long it takes to fill the pipeline. The more demand for one caliber the longer that line will be kept running and production of other, less popular, calibers will be put on the back burner.
It costs time and money to change a line over, and that cost is passed on to the customer in the price of the ammo. The longer a line runs a given caliber, the more the cost will be distributed over a larger number of production units (rounds) and the less the cost will be at the gun shop.
So in many ways, the caliber does influence the cost, but not in the way many folks think.
Does "greed" play a role? Only in that ammunition companies like to make money. There is an alternative - government ownership of all production so "they" can decide what products the public will be allowed to have.
Dahermit can have his opinion, but of the alternatives, I prefer greed.
Jim