yeah i think it boils down to the n3DS XL not being released in the US for about a year, then being discontinued, but even here in the UK where they were released i have seen a lot more XL than standard n3DS consoles, i guess people just prefer feeling like they were getting more for the money as the price difference wasn't too substantial iirc, and the people that would take that discount if they were buying for children etc would probably just buy a standard 3DS/3DSXL rather than the smaller n3ds
as always with these questions it always boils down to supply and demand, limited supply and limited demand in the case of the small n3ds consoles