If DS was a fluke where's the "inevitable" handheld decline?

[Teeqoz]

The GBA sold a lot faster than the 3DS, and would've passed 100 million easily if it had gone as long without a successor as the 3DS had. The DS launched only 3 and a half years after the GBA did. Meanwhile, the 3DS launched nearly 6 years ago and is still about 20 million behind the 3DS...