No one, but neither do you. You keep pontificating about Apple being a design-centric company, as if it was some kind of deep revelation that no one knew about.. However, you fail to explain what in your opinion would constitute deviation from Apple's design principles, if they added backlighting to BT keyboard. I am looking at Logitech Apple keyboard, and it's perfectly well designed. MacBook Air keyboard is perfectly well designed. This has nothing to do with "design".
I have my desktop in a den, and sometimes I like to use it during the early morning and late night without turning on the room lights. I like to keep my desk minimalistic and I don't want a desk lamp. Clearly, there are reasons why some people want this feature from their keyboards - else we wouldn't see Logitech, Microsoft and many others making them.
I don't understand why people keep arguing that just because they don't need backlighting in their keyboards, no one else should need it either!
That's silly. OP can buy one of several backlit keyboards by other vendors. I personally will be getting Logitech EasySwitch keyboard when it ships.