The same reason Apple Doesn't sell an iPhone Zero in the US with a single core processor and 64MB of RAM.
The US is a mature product.
High end brands don't sell sub-lowend products.
But then it means that Americans are overpaying by buying capacity they don't really need. This is something I'm always wondered at, as in the 3rd world even well-off people try to minimize their expenses.
But we do need it. Look at traffic on our highways. You need power to safely merge in many places.