I think this is why:
1st: They learn what the market is like and get acclamted.
2nd: They apply everything they learned from their experience, and their competitors to make the product they know people want.
3rd: They did so much better from 1 -> 2, that they assume if they double down on older policies it will happen again.
*I honestly wouldn't be surprised if it was a cycle (Notice Gamecube -> Wii -> Wii U)
*They don't necessarily fail with the third one, but they sell far less than their second gen...