I am guessing one reason for the FBA program is it allows them to scale up their logistics operation larger than it would otherwise be, and that helps them lowe

I am guessing one reason for the FBA program is it allows them to scale up their logistics operation larger than it would otherwise be, and that helps them lower the cost per item and out-compete other companies. Remember, Amazon's long-term goal is to take over the world, and it needs to do all sorts of things to get there.