I think it’s partially a local inventory issue but more importantly reduces the chance the customer will accidentally order the wrong thing, at the cost of making an unusual case more complicated.
I wonder if beyond local inventory, there is a repair/support aspect to it.
On the confusion part, I once went through phone support back and forth to get a BTO with a different keyboard. It didn't work, and I didn't get much info beyond shrugs. They basically tried to pass the order to the JP branch and it didn't pan out.
