Adding an additional Circle Pad on the Nintendo 3DS XL would have made the system too big according to Nintendo president Satoru Iwata. Iwata says that attaching a second Circle Pad to the Nintendo 3DS XL would have been technically possible, but it would ultimately have made the handheld a lot bigger than it needed to be.
“Attaching a second analog stick is possible but it would have made the system even bigger and, though it perhaps puts a burden on people that really want that second stick, it’s a call we had to make.”
“The choice, if we were going to include the second analog stick, was to reduce the size of the battery or make the unit much bigger. ”