Why Nintendo does`nt give the 3ds xl a second circle pad

Nintendo reveals why they did not add a second circle pad to the new 3ds xl.

Nintendo UK manager Ben Taylor has told us the reason of the lack of second circle pad:
"We did review the possibility of the second controller, but we felt that increased battery life was really important to players, and this would have been affected if we had introduced one. It would also have made the console a lot bigger and bulkier."

So in easier words, because the battery life would be too short and it would be too big and bulky.
But Nintendo is working on a circle pad pro for 3ds xl.