This, it`ll take some time to rebuild those markets - after all the DS and the PSP was the by far the most popular handheld generation. 3DS was dead after it launch and just at the end of last year it started to fulfill expectations, you cant just jump from a +30 million handheld which is owned by everyone to the 3DS and expect the sales to be the same for ever IP. We are still pretty early in the 3DS life cycle, the system still need time to mature and for 3rd partys to see what works and what doesnt.
There are still many people waiting on the 3DS redesign and Nintendo is hoarding their big casual games. Animal Crossing, Brain Training and Co. were all released before more bigger "classic" title were released, this time is different and we are still waiting on real big casual hits to be released. As i said before, for me KH is an IP with strong casual appeal which would have benefited from being released on a bigger userbase.